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Variable-gain amplifier

A variable-gain amplifier (VGA), also known as a voltage-controlled amplifier (VCA) or programmable gain amplifier (PGA), is an electronic device that amplifies an input signal while allowing its gain to be dynamically adjusted via an external control signal, such as a DC voltage or digital input, to optimize signal levels for subsequent processing.^[1]^[2] VGAs operate on principles similar to fixed-gain amplifiers but incorporate mechanisms for gain variation, often using operational amplifiers (op-amps) in feedback configurations where resistors are switched, potentiometers are adjusted, or digital-to-analog converters (DACs) control feedback paths to achieve precise gain steps, such as binary multiples (1, 2, 4, 8) or decade values (10, 100).^[1]^[2] In voltage-controlled designs, the gain is typically proportional to the control voltage in decibels (dB), enabling linear-in-dB adjustments over wide ranges, like 48 dB, while transistor-based implementations allow switching between discrete gain levels using control signals.^[1]^[3] Key design considerations include minimizing noise (e.g., as low as 1.65 nV/√Hz at 1 kHz), ensuring high bandwidth, and achieving low gain error (e.g., 0.02%), with challenges in settling time and switch on-resistance affecting performance.^[1] These amplifiers are essential in applications requiring dynamic range extension, such as automatic gain control (AGC) loops in receivers, where they maintain optimal signal amplitudes despite varying input levels.^[1] Common uses include instrumentation systems for sensor signal conditioning, photodiode preamplifiers in optical detection, ultrasound and sonar front-ends for medical and underwater imaging, and driving analog-to-digital converters (ADCs) in data acquisition to prevent saturation or underutilization.^[1]^[2] In audio processing, VGAs facilitate level compression and amplitude modulation, while in RF/IF circuits, they support swept-gain functions for signal analysis without direct level measurement.^[2]^[4] Integrated VGAs in modern ADCs, like those in the AD77xx series, further enhance system efficiency by combining amplification and digitization.^[1]

Fundamentals

Definition

A variable-gain amplifier (VGA) is an electronic amplifier that varies its gain depending on a control signal, such as a voltage, current, or digital input, to dynamically adjust the amplitude of an input signal.^[5]^[6] This capability distinguishes VGAs from fixed-gain amplifiers, which maintain a constant amplification factor determined by passive components like resistors, without provision for real-time adjustment.^[7] The primary purpose of a VGA is to optimize signal levels across wide dynamic ranges, enabling adaptation to fluctuating input conditions while preventing issues such as clipping from overload or excessive noise from weak signals.^[5]^[6] VGAs play a key role in automatic gain control (AGC) systems by automatically scaling output to maintain consistent signal strength.^[6] In terminology, the gain of a VGA is typically expressed in decibels (dB), providing a logarithmic measure of amplification that aligns with the linear-in-dB response often used for control.^[5] Control signals can be analog, such as a varying voltage that adjusts gain continuously, or digital, using binary codes for discrete steps.^[5] Common abbreviations include VGA for variable-gain amplifier and VCA for voltage-controlled amplifier, the latter emphasizing analog voltage-based control.^[5]

Operating Principles

A variable-gain amplifier (VGA) adjusts its amplification factor through mechanisms such as modulation of transconductance in active devices, variation of feedback elements, or multiplication within the signal path. In transconductance-based approaches, the gain is altered by changing the transconductance (g_m) of transistors via bias current or voltage adjustments, where g_m directly influences the conversion of input voltage to output current. Multiplication techniques, often employing structures like the Gilbert cell, enable gain control by scaling the input signal with a control parameter, providing linear or exponential variation depending on the implementation.^[6]^[8]^[5] For analog control, a control voltage (V_c) modifies the bias of active devices, such as MOSFETs or BJTs, to vary g_m and thus the overall gain. This results in a continuous gain adjustment, often linear in decibels relative to V_c, allowing precise tuning for applications requiring smooth transitions. In digital control, gain is selected in binary or stepwise increments through switching networks or lookup tables that activate discrete transconductance segments or attenuators, enabling programmable operation without analog precision demands.^[6]^[5]^[1] The general gain expression for a VGA can be approximated as G = G_{\max} \cdot f(V_c), where G_{\max} is the maximum gain and f(V_c) is a transfer function (typically between 0 and 1) dependent on the control voltage. From the transconductance relation, start with A_v = g_m R_L, substitute g_m \approx \mu C_{ox} \frac{W}{L} (V_{GS} - V_T) for MOSFETs in strong inversion, and normalize such that f(V_c) = \frac{V_c - V_{\min}}{V_{\max} - V_{\min}}, yielding gain linear in V_c. For a linear-in-dB response, G(\mathrm{dB}) = G_{\max}(\mathrm{dB}) + S \cdot V_c, where S is the slope in dB/V, the transfer function f(V_c) must instead be exponential, as achieved through exponential control in translinear circuits or approximations in multiplier designs.^[5]^[6]^[8] Negative feedback loops in VGAs incorporate variable resistors, capacitors, or attenuators to stabilize gain and bandwidth while enabling controlled variation. By placing a variable element in the feedback path, the closed-loop gain becomes G = \frac{Z_f}{Z_i}, where Z_f and Z_i are adjustable impedances, ensuring low distortion and consistent performance across gain settings.^[1]^[8]^[6] VGAs typically extend the effective input dynamic range by 20-60 dB, accommodating signals from microvolts to volts without saturation or excessive noise, which is essential for maintaining signal integrity in systems with varying input amplitudes.^[1]^[8]^[5]

Types

Analog Variable-Gain Amplifiers

Analog variable-gain amplifiers (VGAs) achieve continuous gain adjustment through analog control mechanisms that modulate the amplification of input signals without digitization, relying on components such as transistors and multipliers to vary resistance, transconductance, or current drive.^[9] These designs operate on the principle of gain modulation by altering circuit parameters in response to a control voltage, enabling smooth transitions across a wide dynamic range.^[1] A primary type of analog VGA is the voltage-controlled amplifier (VCA) that utilizes field-effect transistors (FETs) to provide variable resistance in the signal path. In such configurations, a shunt FET acts as a voltage-variable resistor in a divider network, where the control voltage adjusts the FET's channel resistance to attenuate or amplify the signal; for instance, multiple parallel FETs can be biased to form a composite variable shunt for finer control.^[10] Bipolar transistor-based VCAs, in contrast, modulate transconductance by varying the transistor's bias, converting input voltage differences into proportional output currents that scale with the control signal, offering high linearity in transconductance variation.^[11] Multiplier-based analog VGAs often employ Gilbert cell topologies, which use cross-coupled differential pairs of bipolar transistors to perform four-quadrant multiplication, enabling dB-linear gain control where the gain in decibels is approximately proportional to the control voltage. The gain expression for such a design is given by

G_{\text{dB}} = k \cdot V_c

where k is the sensitivity factor determined by the cell's geometry and biasing, and V_c is the control voltage; this exponential characteristic ensures uniform dB steps for logarithmic signal handling.^[12] The Gilbert cell's differential structure provides excellent linearity and common-mode rejection, making it suitable for wideband applications.^[13] Operational transconductance amplifiers (OTAs) represent another key analog VGA approach, where gain is varied by adjusting the bias current that sets the transconductance g_m, typically implemented with a differential input pair of bipolar transistors whose collector currents are steered based on the input voltage difference. The output is a current I_{\text{out}} = g_m \cdot (V_+ - V_-), with g_m \propto I_{\text{bias}}, followed by current-to-voltage conversion using an external load resistor R_L to yield V_{\text{out}} = -I_{\text{out}} \cdot R_L, allowing gain A_v = g_m \cdot R_L to be tuned linearly with I_{\text{bias}} via a control voltage that generates the bias.^[9] OTAs typically require output buffering to convert current to voltage and ensure proper voltage compliance, with careful design for stability.^[14] Analog VGAs offer advantages including smooth, continuous gain adjustment without discrete steps and wide bandwidths extending to hundreds of MHz, preserving signal integrity in real-time applications.^[15] Historically, analog VGAs evolved to integrated circuits like those from THAT Corporation, which introduced transistor-based VCAs such as the dbx 202 for professional audio mixing with improved linearity and dynamic range.^[16] Performance metrics unique to analog designs include settling time for gain changes, typically on the order of microseconds, reflecting the time for internal nodes to stabilize after control voltage updates.^[1]

Digital Variable-Gain Amplifiers

Digital variable-gain amplifiers (VGAs) implement gain adjustment through discrete, programmable steps, typically integrated within digital signal processing (DSP) chains or mixed-signal systems, enabling precise control without the continuous variation found in analog counterparts.^[1] A primary method involves DSP-based multiplication, where the output signal is generated as y = G_{\text{digital}} \cdot x, with G_{\text{digital}} as a quantized coefficient selected from a finite set of values.^[17] This approach leverages the multiply-accumulate operations inherent in DSP architectures, but introduces quantization effects, where the finite precision of G_{\text{digital}} leads to rounding errors that manifest as additive noise in the output spectrum.^[18] Digital potentiometers and switched attenuators form another key implementation, employing resistor ladders or capacitor arrays to achieve selectable gain steps. In resistor-ladder designs, a series of fixed resistors is tapped by CMOS switches to form variable voltage dividers, while capacitor arrays use switched-capacitor techniques for sampled-data systems, both providing attenuation or amplification ratios. These elements are controlled via digital interfaces such as serial peripheral interface (SPI) or parallel buses, allowing external microcontrollers or DSPs to set gain values dynamically with minimal pin count.^[19] Programmable gain amplifiers (PGAs), a specialized subset of digital VGAs, offer gain settings in increments of 1-6 dB, commonly spanning ranges up to 60 dB, and are widely integrated into analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) to optimize dynamic range.^[20] For instance, devices like the AD8285 provide 16 dB to 34 dB gain in 6 dB steps via SPI programming, while others achieve finer 0.5 dB resolution over ±12 dB for audio or sensor applications.^[21] These PGAs ensure input signals fit the converter's full scale, preventing clipping or underutilization. The advantages of digital VGAs include precise, repeatable gain settings determined by code rather than analog parameters, immunity to temperature-induced drift and power supply variations, and seamless integration into system-on-chips (SoCs) alongside other digital logic.^[1] Examples include dedicated integrated circuits like Analog Devices' AD8260, a dual-channel digitally programmable VGA with serial interface for RF and instrumentation designs. Unique challenges in digital VGAs arise from the quantization noise floor, which limits the signal-to-noise ratio (SNR) based on coefficient bit depth—typically degrading SNR by 6 dB per bit reduction—and aliasing in oversampled architectures, where insufficient anti-aliasing filtering before gain application can fold high-frequency noise into the baseband.^[18] Mitigation often involves higher-resolution coefficients or noise-shaping techniques, though these increase computational overhead in DSP realizations.^[22]

Applications

In Audio Systems

Variable-gain amplifiers (VGAs), commonly realized as voltage-controlled amplifiers (VCAs), are essential in sound mixing consoles for enabling precise fader control of channel gain without routing audio signals through the faders themselves. Instead, faders generate control voltages that modulate the VCAs in the channel strips, facilitating automated mixing and dynamic level adjustments across multiple channels. This architecture was pioneered in Solid State Logic (SSL) consoles, with the 4000 series introducing VCA faders in 1981, allowing computer-assisted automation that revolutionized professional recording workflows in the 1980s.^[23]^[24] In audio compressors and limiters, VGAs operate within feedback loops to deliver automatic gain reduction, detecting signal levels and applying proportional attenuation to prevent overload and clipping. The control voltage from the sidechain detector modulates the VCA, enabling adjustable attack, release, and ratio parameters for tailored dynamic control in professional applications. This integration ensures transparent processing with minimal coloration, as seen in classic designs using early dbx VCAs that evolved into modern IC-based solutions for improved fidelity.^[16]^[25] A key example is the THAT 2180 series VCA chip, widely adopted in professional audio for its exponential gain control, >120 dB dynamic range, and THD below 0.01% at 1 kHz, supporting high-headroom applications like faders and compressors.^[26] In multi-channel setups, VCAs minimize crosstalk by separating the low-level control path from the audio signal path, reducing inter-channel interference while preserving headroom through low-noise operation and precise gain scaling.^[27]^[16] The evolution toward digital audio has shifted some VGA functions to DSP implementations in digital audio workstations (DAWs), where virtual VCA groups enable plugin-based gain automation for efficient control of track levels and dynamics without analog hardware.^[28]^[29]

In Communications

In communication systems, variable-gain amplifiers (VGAs) play a crucial role in receivers by forming the core of automatic gain control (AGC) loops, which dynamically adjust the gain to maintain a constant output signal level despite fluctuations in input power levels, such as those caused by fading or varying distances in wireless channels.^[7] This stabilization is essential for preventing receiver overload or insufficient signal strength, particularly in cellular base stations where input signals can span wide dynamic ranges from strong nearby transmissions to weak distant ones.^[30] For instance, in a W-CDMA receiver design operating at an IF frequency of 380 MHz, VGAs integrated with true-RMS detectors ensure waveform-independent output power, optimizing adjacent channel power ratio (ACPR) performance.^[30] In RF front-ends, VGAs often function as variable attenuators to enhance linearity, especially in high-frequency applications like 5G millimeter-wave (mmWave) systems, where they provide a dynamic range of 30-50 dB to handle the challenges of beamforming and high path loss.^[31] These amplifiers are typically placed after low-noise amplifiers to prevent saturation while preserving signal-to-noise ratio, as seen in Ka-band reconfigurable dual-band VGAs operating from 23.5-40.5 GHz, which maintain low phase variation across gain settings for phased-array transceivers.^[32] In such systems, the VGA's ability to adjust gain in small steps ensures compliance with linearity demands under varying modulation schemes like OFDM. For baseband processing in modems, digital VGAs enable adaptive gain control as part of equalization stages, where algorithms such as least mean squares (LMS) iteratively adjust coefficients to compensate for channel distortions and normalize signal amplitudes.^[33] This integration allows real-time adaptation to inter-symbol interference in high-speed links, with digital implementations offering precise control via DSPs in quadrature (I/Q) channels. A specific example is their use in Wi-Fi chipsets like those from Qualcomm Atheros, where VGAs employ received signal strength indicator (RSSI)-based control to dynamically scale gain for optimal demodulation across 802.11 standards, reducing bit error rates in multipath environments.^[34] Performance requirements for VGAs in communications emphasize high linearity, with third-order input intercept points (IIP3) exceeding 20 dBm to minimize intermodulation distortion in multi-carrier scenarios, as demonstrated by designs achieving up to 24 dBm IIP3 in multi-standard receivers covering WLAN and cellular bands.^[35] Additionally, fast settling times are critical for handling bursty signals in time-division duplex systems like TD-SCDMA, where AGC loops must stabilize quickly to avoid preamble loss, often achieved through log-domain detectors for signal-independent response.^[36]

In Instrumentation and Imaging

Variable-gain amplifiers (VGAs) play a crucial role in instrumentation systems, particularly in data acquisition setups where they provide programmable gain to amplify weak sensor signals while optimizing signal-to-noise ratio (SNR). In applications involving sensors like strain gauges, which produce millivolt-level outputs from mechanical deformations, VGAs enable precise scaling of these signals to match the input range of downstream analog-to-digital converters (ADCs), typically offering gains from 1 to 1000 to accommodate varying signal amplitudes without introducing excessive noise or distortion.^[37]^[38] This programmability is essential for maintaining high accuracy in static measurements, such as structural health monitoring, where environmental factors can alter sensor sensitivity.^[39] In biomedical instrumentation, VGAs enhance the handling of bio-signal variability, as exemplified by Analog Devices' AD8421, a low-noise instrumentation amplifier used in electrocardiogram (ECG) systems to amplify subtle cardiac potentials ranging from microvolts to millivolts. The AD8421 achieves gains from 1 to 10,000 via a single external resistor, allowing adaptation to patient-specific signal strengths while preserving signal integrity through its ultralow input bias current (1 nA max) and high common-mode rejection ratio (up to 140 dB).^[40] By boosting weak signals early in the chain, such VGAs improve overall system resolution, effectively reducing the number of ADC bits required for equivalent dynamic range—for instance, a 10x gain can extend an 8-bit ADC's effective resolution in low-signal scenarios by minimizing quantization noise.^[1]^[41] In imaging systems, VGAs facilitate exposure control within camera pipelines, particularly in CMOS sensors where they adjust pixel-level gain to compensate for varying light conditions or tissue depths. For medical ultrasound imaging, VGAs in the receiver front-end amplify echoes from deep tissues, which attenuate more than superficial ones, ensuring uniform image brightness via time-gain compensation (TGC) that ramps gain exponentially with depth.^[42]^[43] In general CMOS image sensors, column-level or pixel-adaptive VGAs dynamically scale signals to prevent saturation in bright areas while enhancing detail in low-light regions, thereby improving contrast and reducing noise in applications like endoscopy.^[44]^[45] This adaptability is particularly beneficial in weak-signal environments, where VGAs can double effective sensitivity without increasing sensor size or power draw.^[46] Hybrid approaches combining analog VGAs with digital fine-tuning are common in both instrumentation and imaging pipelines, where the analog stage provides coarse gain adjustment pre-digitization to handle high dynamic ranges, followed by digital processing for precise corrections. In ultrasound receivers, for example, an analog VGA amplifies the raw RF signal before ADC conversion, with digital gain stages then applying TGC profiles to refine the image without analog settling delays.^[47] Similarly, in data acquisition systems, programmable gain instrumentation amplifiers (PGIAs) use analog multiplication for initial boosting of sensor outputs, enabling digital control to optimize SNR across multiplexed channels.^[37] This combination leverages the low-noise benefits of analog processing while allowing flexible post-processing, ultimately enhancing resolution in low-light or weak-signal scenarios by better utilizing ADC capacity.^[1]

Design and Implementation

Key Considerations

In variable-gain amplifier (VGA) design, linearity and distortion are paramount, particularly for applications requiring signal fidelity. Total harmonic distortion (THD) and intermodulation distortion (IMD) are key metrics, with typical goals of less than 0.1% THD (equivalent to -60 dBc) and comparable IMD levels for audio and RF systems to minimize nonlinear effects. For instance, the THS7530 VGA achieves HD3 of -61 dBc and IMD3 of -62 dBc at 32 MHz and 70 MHz, respectively, demonstrating low distortion under high-speed conditions. Gain steps in discrete-control VGAs can exacerbate intermodulation products if not finely resolved, as abrupt transitions introduce transient nonlinearities that generate spurious frequencies.^[48] Noise figure (NF) in VGAs varies significantly with gain settings, influencing overall system sensitivity in cascaded stages. At high gain, the NF is dominated by the input stage, but reducing gain amplifies downstream noise contributions, often increasing NF by 10-20 dB across the control range. This is analyzed using the Friis formula for cascaded noise factors: F_{\text{total}} = F_1 + \frac{F_2 - 1}{G_1} + \frac{F_3 - 1}{G_1 G_2} + \cdots, where F denotes noise factor and G is power gain; in VGA-inclusive receivers, a 10 dB gain reduction can elevate the total NF from ~3 dB to over 10 dB if the VGA precedes noisy elements like mixers. Examples include the AD600 series with a constant 1.4 nV/√Hz input noise density, yielding an NF of 5.3 dB at maximum gain (Rs = 50 Ω), but rising sharply at lower settings.^[49] Bandwidth and slew rate present critical trade-offs in high-speed VGAs, especially for RF applications exceeding 1 GHz. Wider bandwidth enables broader signal handling but often reduces gain flatness and increases power draw, while slew rate determines transient response, with settling times governed by t_s \approx \frac{[\Delta V](/page/Delta-v)}{[SR](/page/SR)} \ln\left(\frac{1}{[\epsilon](/page/Epsilon)}\right), where [SR](/page/SR) is slew rate, \Delta V is output step, and \epsilon is error tolerance. Devices like the AD8368 offer 800 MHz bandwidth with a slew rate supporting rapid gain changes, but for high-speed applications like the AD8370 with 750 MHz bandwidth, compensating for parasitic capacitances limits slew rate to 5.75 V/μs, balancing speed against stability.^[50]^[51] Power consumption in VGAs differentiates between dynamic (signal-dependent) and static (bias-related) components, with analog designs favoring efficiency in battery-powered devices through low quiescent currents. Analog VGAs typically consume 3-50 mA dynamically, scaling with gain and bandwidth, while digital variants add static power from control logic, potentially 20-50% higher overall. For example, the AD8338 draws ~3 mA at mid-gain (40 dB) in a 5 V supply, enabling extended battery life in portable RF systems with its low quiescent current.^[52] Control range and accuracy define VGA versatility, with typical ranges of 40-100 dB to accommodate wide dynamic signals, and dB-linearity error targeted below 0.5 dB for precise attenuation. The AD600 achieves ±0.2 dB error over 40 dB, while advanced designs like a 65 nm CMOS VGA attain 0.4 dB error across 62.4 dB, ensuring monotonic gain response without calibration. Step sizes of 0.5-1 dB maintain accuracy, though finer resolution (e.g., 0.125 dB in some digitally controlled units) trades off against increased complexity.^[49]^[53]

Circuit Topologies

One common circuit topology for variable-gain amplifiers (VGAs) employs degenerative feedback, where a variable resistor is placed in the feedback path of an operational amplifier configured in a non-inverting arrangement to achieve linear gain control.^[54] This approach leverages negative feedback to stabilize the gain, with the voltage gain given by A_v = 1 + \frac{R_f}{R_{in}} where R_f is the variable feedback resistor and R_{in} is the fixed input resistor; varying R_f (e.g., via a potentiometer, FET, or digitally controlled resistor) directly modulates the gain linearly.^[55] This topology offers simplicity and good linearity for low-frequency applications but may suffer bandwidth limitations at high frequencies due to the feedback network.^[54] Another prevalent architecture is the current-steering topology, typically implemented using differential pairs where the tail current is varied to control gain.^[56] In this design, the transconductance (g_m) of the input pair is adjusted by steering a portion of the bias current away from the signal path, resulting in an approximately exponential gain variation that approximates dB-linear control.^[57] For instance, the gain can be expressed as proportional to \sqrt{I_{tail}}, where I_{tail} is the variable tail current, enabling wide dynamic range with minimal phase shift across gain settings.^[57] This topology maintains constant input linearity and is favored in RF and mm-wave systems for its high-speed performance.^[56] Hybrid topologies combine elements of analog and digital processing for enhanced flexibility, such as an analog multiplier core followed by a fixed-gain amplifier stage.^[58] Here, the multiplier (e.g., a Gilbert cell) performs the gain adjustment by multiplying the input signal with a control voltage, providing smooth analog control, while the subsequent amplifier boosts the output without altering the gain profile.^[58] Alternatively, digital multipliers in a DSP block can compute the gain factor, with the result converted via a DAC to drive an analog VGA stage, enabling precise, programmable control in mixed-signal systems.^[54] Integrated circuit examples illustrate these topologies in practice; the LMH6518 from Texas Instruments is a broadband VGA employing a digitally controlled ladder attenuator in a differential architecture, achieving a 40 dB gain range in 2 dB steps with 900 MHz bandwidth suitable for ADC drivers and RF/IF applications.^[59] For optical receivers, hybrid topologies are common, such as those using current-steering in transimpedance amplifiers with variable gain to handle dynamic optical power levels.^[60] Simulation and prototyping of VGAs often rely on SPICE models to characterize gain versus control voltage curves, allowing verification of linearity and bandwidth before fabrication.^[61] For example, transient or AC analyses in tools like LTspice can plot gain response against varying control parameters, revealing potential distortions or stability issues in topologies like current-steering designs.^[61]

References

[1]
[PDF] MT-072 TUTORIAL | Precision Variable Gain Amplifiers (VGAs)
Figure 1: Variable Gain Amplifier (VGA) Applications. Such a device has a gain that is controlled by a dc voltage or, more commonly, a digital input. This ...Missing: principles | Show results with:principles
[2]
Activity: Variable Gain Amplifiers - Analog Devices Wiki
Jan 3, 2021 · A variable-gain or voltage-controlled amplifier is an electronic amplifier that varies its gain depending on a control voltage.Missing: principles | Show results with:principles
[3]
[PDF] Dual, Low Noise, Single-Supply Variable Gain Amplifier AD605
Each independent channel of the AD605 provides a gain range of 48 dB that can be optimized for the application. Gain ranges between −14 dB to +34 dB and 0 dB to ...Missing: principles tutorial
[4]
[PDF] CHAPTER 4 RF/IF CIRCUITS - Analog Devices
Many monolithic variable-gain amplifiers use techniques that share common principles that are broadly classified as translinear, a term referring to circuit ...
[5]
[PDF] Variable Gain Amplifiers - Analog Devices
What are VGAs? Variable gain amplifiers (VGAs) are signal-conditioning amplifiers with elec- tronically settable voltage gain. There.Missing: definition | Show results with:definition
[6]
[PDF] Lecture 25: Variable Gain Amplifiers (VGAs)
Variable gain amplifiers (VGAs) are employed to maximize system dynamic range and are a critical component of automatic-gain control (AGC) systems.Missing: definition | Show results with:definition
[7]
[PDF] MT-073: High Speed Variable Gain Amplifiers (VGAs)
The concept is simple: a fixed-gain amplifier follows a passive, broadband attenuator equipped with special means to alter its attenuation under the control of ...<|control11|><|separator|>
[8]
[PDF] A Review on Variable and Programmable Gain Amplifiers and ...
They are key components in front-end analog conditioning circuits for measurement, since many sensors output voltage or current signals of usu- ally small ...
[9]
[PDF] Demystifying the Operational Transconductance Amplifier (Rev. A)
Used as a basic building block, an OTA element simplifies designs of automatic gain control (AGC) amplifiers, light-emitting diode (LED) driver circuits, fast- ...
[10]
[PDF] VCA2612: Dual, Variable Gain Amplifier with Low Noise Preamp ...
The attenuator is essentially a variable voltage divider consisting of one series input resistor, RS, and ten identical shunt FETs, placed in parallel and ...
[11]
https://www.renesas.com/en/document/apn/an6077-ic-operational-transconductance-amplifier-ota-power-capability
[12]
https://ieeexplore.ieee.org/document/9366396
[13]
(PDF) Wideband DB-linear VGA for high-speed communications
Apr 3, 2020 · To realize a dB-linear AGC range, a pseudo-folded Gilbert cell driven by a single-branch negative exponential generator (NEG) is proposed as the ...
[14]
Operational Transconductance Amplifier (OTA) - Planet Analog
Aug 17, 2022 · The transconductance is directly proportional to an amplifier bias current (I_abc), which is used to control the transconductance. In real OTA ...
[15]
[PDF] VCA810 High Gain Adjust Range, Wideband and Variable Gain ...
The voltage-controlled gain feature of the VCA810 makes this amplifier ideal for precision AGC applications with control ranges as large as 60 dB. The AGC ...Missing: FET | Show results with:FET
[16]
A Brief History of VCAs - THAT Corporation
The original dbx 202 “Black Can” VCAs, which can still be found in operating consoles today, have been around for over 20 years. These first VCAs suitable for ...
[17]
Controlling a DSP Network's Gain: A Note For DSP Beginners
Mar 29, 2019 · This blog briefly discusses a topic well-known to experienced DSP practitioners but may not be so well-known to DSP beginners.
[18]
Practical Filter Design for Precision ADCs - Analog Devices
Oversampling a signal at twice the Nyquist rate evenly spreads the ADC's quantization noise power into a double frequency band. Then it is easy to design ...
[19]
https://www.ersaelectronics.com/blog/variable-gain-amplifier-ic-guide
[20]
AD8285 Datasheet and Product Info - Analog Devices
Programmable gain amplifier (PGA) Includes low noise preamplifier (LNA) Serial peripheral interface (SPI) programmable gain 16 dB to 34 dB in 6 dB steps ...
[21]
CS4245 | Cirrus Logic
Programmable gain amplifier: ±12 dB gain, 0.5 dB step sizes with zero crossing; Microphone pre-amp with 32 dB gain and low-noise bias supply; Digital volume ...
[22]
(PDF) Review on Variable and Programmable Gain Amplifiers and ...
Aug 6, 2025 · Variable and programmable gain amplifiers have been a recurrent subject of study over the last 50 years, and, are increasingly used in ...
[23]
Dealing with Aliasing and Quantization Errors in DSP - LinkedIn
Mar 15, 2023 · The quantization error introduces noise and distortion in the signal, which depends on the quantization scheme and the signal characteristics.
[24]
Technology - Artisamp
In the 1980s, Solid State Logic (SSL) developed a computer-controllable mixing console that used DBX VCA's for its faders. Their first console, the SSL ...
[25]
VCA Faders and Groups - balancing the balance.
Oct 5, 2016 · On a classic E/G-Series SSL-Console, EVERY large fader is a VCA-Fader. Audio NEVER passes through the faders – the faders just send a control ...
[26]
Feedback Vs. Feed-Forward Compression: The Differences You ...
Nov 7, 2018 · All compressors have a detector circuit (often another VCA itself) which tells the VCA that's doing the compressing to adjust the level.
[27]
[PDF] THAT Corporation 2180 Series Datasheet
The THAT 2180 series are high-performance voltage-controlled amplifiers with wide dynamic range (>120 dB), wide gain range (>130 dB), and low distortion (<0.01 ...
[28]
VCA fader consoles - Gearspace
Nov 26, 2009 · VCA faders are noisy. Get a moving fader automation system if the noise is a problem. Many VCA consoles allow you to swap paths between the small and large ...
[29]
Logic Pro X: How to Create and Use VCA Faders and VCA Groups
Jan 18, 2019 · With a VCA the engineer can control multiple faders in a group with a single fader while preserving the level of each individual channel in the group.
[30]
Gain Staging In Your DAW Software
Gain staging couldn't be simpler: you ensure that you feed an appropriate level from the first stage of your signal path to the next, and repeat this from the ...Missing: VGAs | Show results with:VGAs
[31]
Design and Operation of Automatic Gain Control Loops for ...
May 1, 2003 · This article is intended to provide insight into the effective operation of variable gain amplifiers (VGA) in automatic gain control (AGC) applications.
[32]
https://www.researchgate.net/publication/385359098_A_Ka-Band_Reconfigurable_Dual-Band_Variable_Gain_Amplifier_With_Low_Phase_Variation_for_5G_Communications
[33]
A Ka-Band Reconfigurable Dual-Band Variable Gain Amplifier With ...
Aug 7, 2025 · This paper presents a 23.5-34 GHz and 28-40.5 GHz Ka-band reconfigurable dual-band variable gain amplifier (VGA) for 5G applications, realized in TSMC 28-nm ...
[34]
[PDF] Mixed-Signal and DSP Design Techniques, DSP Applications
High performance modems make use of digital techniques to perform such functions as modulation, demodulation, error detection and correction, equalization, and ...
[35]
US7212798B1 - Adaptive AGC in a wireless network receiver
The receive signal path also includes one or more variable gain amplifiers (VGAs) that are set by an automatic gain control (AGC) system 125 to set the gains of ...
[36]
A 6.4 mW, 4.9 nV/√Hz, 24dBm IIP3 VGA for a multi-standard (WLAN ...
The IIP3 (third order input referred intercept point) of the PGA is measured to be as high as 20dBm at the minimum gain, meanwhile the NF is 28dB when the PGA ...Missing: settling | Show results with:settling<|control11|><|separator|>
[37]
[PDF] Automatic Gain Control (AGC) in Receivers - QSL.net
Variable gain control for the later stages can operate from low signal levels. Variable-gain amplifiers are controlled electrically, and when attenuators are ...
[38]
Programmable Gain Instrumentation Amplifiers: Finding One that ...
Programmable gain instrumentation amplifiers (PGIAs) are used in data acquisition to accommodate sensor sensitivities and optimize signal-to-noise ratio (SNR).
[39]
Fundamentals of Strain Gauge Instrumentation Amplifiers
Feb 3, 2021 · Specifically, these amplifiers provide very low DC offset, low drift, low noise, very high open-loop gain, very high common-mode rejection ...
[40]
Strain Gauge / Bridge Input Signal Amplifiers - GlobalSpec
It features variable gain and output scaling and will accept differential or single-ended inputs. ... The DU1D monitor is an industrial amplifier and monitor for ...
[41]
[PDF] AD8421 data sheet - Analog Devices
The AD8421 is a low cost, low power, extremely low noise, ultralow bias current, high speed instrumentation amplifier that is ideally suited for a broad ...Missing: ADI ECG variable
[42]
Why use gains on an ADC - Electrical Engineering Stack Exchange
May 17, 2021 · The analog gain block matches the range of the signal to the range of the ADC, maximizing the effective resolution and reducing the level of ...Missing: advantages variable light imaging instrumentation
[43]
A Programmable Gain Amplifier with Fast Transient Response for ...
In ultrasound applications, the time gain compensation (TGC) adjusts the PGA gain according to a predefined control profile, requiring fast gain settling within ...
[44]
Programmable Gain Amplifier with Programmable Bandwidth for ...
This paper presents a low-power, fully differential, programmable gain amplifier (PGA) for ultrasound receiver analog front-ends (AFE).
[45]
A high-sensitivity CMOS image sensor with gain-adaptive column ...
Aug 9, 2025 · A low noise and relatively high dynamic range CMOS active pixel sensor (APS) using a variable-gain column amplifier is presented and analyzed.
[46]
Column amplifier with automatic gain selection for CMOS image ...
A column amplifier architecture having automatic gain selection for CMOS image sensors, which reduces the effect of analog noise, while maintaining a system's ...
[47]
Introduction to CMOS Image Sensors - Evident Scientific
... amplifier. The gain of this amplifier is controlled either by hardware or software (and in some cases, a combination of both). In contrast, CMOS image sensors ...
[48]
[PDF] Signal Processing Overview of Ultrasound Systems for Medical ...
Nov 12, 2008 · The resulting low voltage signals are scaled using a variable controlled amplifier (VCA) before being sampled by analog-to-digital converters. ( ...<|separator|>
[49]
[PDF] Handbook of Operational Amplifier Applications - Texas Instruments
Due to the high gain of operational amplifiers, only a very small input voltage then appears at the output and the output is virtually at ground potential. For ...
[50]
A 57–64 GHz low-phase-variation variable-gain amplifier
The phase analysis of current-steering topology reveals the effect of the phase compensation capacitor. The proposed VGA achieves peak gain of 13–15 dB from ...
[51]
A CMOS Low-Distortion Variable Gain Amplifier with Exponential ...
In this paper, a CMOS low-distortion variable gain amplifier with exponential gain control is developed by utilizing a transconductance linearization scheme ...
[52]
[PDF] SECTION 3 RF/IF SUBSYSTEMS Walt Kester, James Bryant, Bob ...
An analog multiplier can be used as a variable-gain amplifier as shown in Figure 3.3. The control voltage is applied to one input, and the signal to the other. ...
[53]
https://research.tudelft.nl/files/139828924/A_0.96_mW_dB_Linear_Variable_Gain_Amplifier_With_0.4_dB_Linearity_Error_Over_a_62.4_dB_Gain_Tuning_Range.pdf
[54]
Variable Gain Amplifiers (VGA) - Analog Devices
Applications ranging from ultrasound, radar, LIDAR, wireless communications, and speech analysis have utilized VGAs to deliver industry leading performance.Missing: examples | Show results with:examples<|control11|><|separator|>
[55]
SPICE simulation of Wideband Variable Gain Amplifier VCA820
The VCA820 is a voltage controlled gain amplifier. The gain can be set with two external resistors, the gain resistor Rg and the feedback resistor Rf.