Variable Gain Amplifier Circuit With Linear Voltage-to-Current Control
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Solution Overview
Problem
Existing voltage controlled variable gain amplifier circuits do not vary their gain linearly and continuously with respect to the gain control voltage, and are susceptible to power supply voltage, semiconductor manufacturing process, and temperature variations.
Innovation Solution
A voltage controlled variable gain amplifier circuit is designed with a first differential amplifier, a second differential amplifier, a gain control voltage/current conversion circuit, and a current bypass circuit, where the gain control voltage is converted into a linearly varying current to control the gain, and a reference current generation circuit that suppresses power supply voltage dependence, using a constant gm type reference current generation circuit to minimize manufacturing and temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a voltage controlled variable gain amplifier circuit is designed to vary gain continuously, then gain controllability is improved, but the gain varies logarithmically rather than linearly with control voltage
Solution Approach 1:
The patent changes the control parameter relationship by converting the control voltage to a control current that varies linearly with the voltage, rather than using the voltage directly. This linear current control enables the gain to vary linearly with the control voltage, resolving the non-linear logarithmic relationship in conventional circuits.
Solution Approach 2:
The patent introduces a current control mechanism as an intermediary between the voltage control input and the gain adjustment. The control voltage is converted to a control current that linearly modulates the amplifier gain, acting as a mediator that transforms the non-linear voltage-gain relationship into a linear one.
2Device complexity
If conventional voltage controlled amplifier circuits are used, then circuit simplicity is maintained, but the gain depends on power supply voltage variations
Solution Approach 1:
The patent employs feedback mechanisms where a portion of the output signal is fed back to the control input to compensate for power supply variations. This feedback loop automatically adjusts the gain to maintain stability despite changes in power supply voltage, improving reliability without significantly increasing circuit complexity.
3Ease of manufacture
If standard amplifier designs are used, then manufacturing simplicity is maintained, but the gain exhibits variations due to semiconductor manufacturing processes and temperature
Solution Approach 1:
The patent uses feedback circuits that sense the actual gain and automatically adjust to compensate for manufacturing variations and temperature effects. This closed-loop approach reduces sensitivity to component tolerances and environmental conditions, achieving stable gain without requiring high-precision manufacturing.
Data Source
AI summary
This invention provides a voltage controlled variable gain amplifier circuit that varies its gain linearly and continuously against a gain control voltage VC. The voltage controlled variable gain amplifier circuit includes a first differential amplifier, a second differential amplifier, a gain control voltage/current conversion circuit and a reference current generation circuit. The first differential amplifier and the second differential amplifier are connected in series. The gain control voltage/current conversion circuit converts the gain control voltage VC into a gain control current IC that varies linearly against the gain control voltage VC. Drain currents Id1 and Id2 of first and second differential input transistors vary linearly against the gain control current IC.