Variable Gain Amplifier With Phase-Inversion Limit Control
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Solution Overview
Problem
The change in operating point of the Gilbert cell circuit is small, leading to suppressed frequency characteristics when gain is changed, and adjusting gain in a four-quadrant Gilbert cell type variable gain amplifier can result in output phase inversion.
Innovation Solution
A variable gain amplifier circuit with a main circuit that includes a differential current circuit, a current divider circuit, and a load circuit, along with a gain adjustment circuit that generates control voltages and limits the voltage difference to prevent phase inversion by maintaining the amplitude of differential output voltage signals above a setting voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If gain is adjusted in a four-quadrant Gilbert cell type variable gain amplifier, then the gain can be changed, but the output phase may be inverted
Solution Approach 1:
The patent applies preliminary anti-action by using a limit circuit to preemptively prevent the control voltage difference from becoming zero or negative, which would cause phase inversion. The limit circuit ensures the voltage difference remains above a predetermined threshold before it can cause harmful phase inversion effects.
Solution Approach 2:
The patent implements feedback by using an amplitude detection circuit to monitor the amplitude of differential output voltage signals and feed this information back to the limit circuit. The limit circuit then adjusts the control voltages based on this feedback to maintain amplitude above a setting voltage and prevent phase inversion.
2Adaptability or versatility
If the voltage difference between control voltages is increased to adjust gain, then the gain changes, but the amplitude of differential output voltage signals may become lower than setting voltage
Solution Approach 1:
The amplitude detection circuit continuously monitors the output signal amplitude and provides feedback to the limit circuit. When the amplitude falls below the setting voltage, the feedback mechanism triggers the limit circuit to adjust the control voltages, ensuring the amplitude remains above the threshold while maintaining gain control capability.
Solution Approach 2:
The patent employs dynamic control by making the control voltages adjustable based on real-time amplitude conditions. The limit circuit dynamically modifies the control voltages in response to amplitude variations, allowing the system to adaptively maintain reliable output amplitude while enabling gain adjustment.
Data Source
AI summary
A variable gain amplifier circuit includes a main circuit including a differential current circuit, a current divider circuit connected to a high potential side of the differential current circuit, and a load circuit connected to a high potential side of the current divider circuit, the main circuit being configured to generate differential output voltage signals by the load circuit in accordance with either differential input voltage signals or first differential current signals; and a gain adjustment circuit configured to adjust a gain of the main circuit. The gain adjustment circuit includes a generation circuit configured to generate a first control voltage and a second control voltage in accordance with a setting signal, and a limit circuit configured to limit, by detecting an amplitude of the differential output voltage signals, the voltage difference to a limit value or greater so that the amplitude does not become lower than a setting voltage.