Rectifying Circuit Using Transconductance Modulation to Eliminate DC Offset
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Solution Overview
Problem
Existing full-wave rectifying circuits face challenges with high current consumption and significant DC offset currents due to diode threshold errors and the need for large bias currents to achieve high-frequency signal amplification, which limits their efficiency and output amplitude.
Innovation Solution
The proposed rectifying circuit employs a voltage-current converting unit with a two-stage operational amplifier and class AB output circuit, using negative feedback to separate bias currents from signal currents, and incorporates a current inverting unit to achieve full-wave rectification with reduced offset and low current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a full-wave rectifying circuit uses a differential amplifier and Gm cell with diodes, then rectification function is achieved, but DC offset current increases due to diode threshold errors
Solution Approach 1:
The patent extracts the rectification function from the diode-based differential amplifier and implements it separately using a Gm cell with transconductance modulation. The Gm cell converts the input voltage to a current that is then rectified by controlling the transconductance parameter, separating the rectification mechanism from the threshold-voltage-dependent diode operation, thereby eliminating DC offset current.
Solution Approach 2:
The patent changes the operating parameter from voltage (diode threshold voltage) to transconductance (Gm). By modulating the transconductance parameter of the Gm cell according to the input signal polarity, the circuit achieves rectification without relying on diode threshold voltages, thus eliminating the source of DC offset current while maintaining rectification function.
2Speed
If large bias currents are used to achieve high-frequency signal amplification, then amplification performance improves, but current consumption increases
Solution Approach 1:
The patent employs periodic switching of the transconductance parameter in the Gm cell to achieve high-frequency signal amplification. By periodically modulating the transconductance at the signal frequency, the circuit can amplify high-frequency signals without requiring continuously large bias currents, thus improving amplification performance while reducing overall current consumption.
Solution Approach 2:
The patent replaces the traditional bias-current-dependent amplification mechanism with a transconductance-modulation mechanism. Instead of relying on large continuous bias currents to achieve high-frequency gain, the circuit uses time-varying transconductance control, substituting a static current-based approach with a dynamic parameter-based approach that achieves the same effect with lower power consumption.
3Reliability
If diodes are used for rectification, then rectification is achieved, but output amplitude is limited due to threshold voltage drops
Solution Approach 1:
The patent changes the rectification mechanism from voltage-based (diode threshold voltage) to current-based (transconductance modulation). By controlling the transconductance parameter of the Gm cell, the circuit can produce large output currents without the limiting effect of diode threshold voltage drops, thereby achieving both rectification and high output amplitude simultaneously.
Data Source
AI summary
A rectifying circuit includes: a voltage-current converting circuit that converts an input voltage into a current; a first transistor and a second transistor that are connected in series and that are connected to a first node into which the current converted by the voltage-current converting circuit flows; a third transistor and a fourth transistor that are connected in series, and that respectively mirror a current flowing through the first transistor and a current flowing through the second transistor; and a first diode that is connected between a second node connected to the third transistor and the fourth transistor, and an output terminal.