Differential Sign-Switching Circuitry Without Neutralization Capacitors
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Solution Overview
Problem
Designing a sign switching circuitry that addresses challenges such as power efficiency, voltage headroom, linearity, gain, and unwanted feedthrough between the input and output.
Innovation Solution
The sign switching circuitry comprises two differential common-source amplifiers with opposite gains, connected through a switching circuitry that activates one amplifier and deactivates the other to achieve sign switching, thereby neutralizing gate-to-drain capacitance without additional capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single common-source amplifier is used for sign switching, then the circuit complexity is reduced, but the gate-to-drain capacitance causes gain loss and instability
Solution Approach 1:
The single amplifier is segmented into two identical common-source amplifiers operating in a push-pull configuration. Each amplifier handles one half of the signal cycle, with their outputs combined through differential signaling. This segmentation allows the gate-to-drain capacitance of one amplifier to be neutralized by the other, resolving the stability issue while maintaining manageable complexity.
Solution Approach 2:
The invention uses the gate-to-drain capacitance of one amplifier to counterbalance the capacitance of the other amplifier. By configuring the amplifiers in a differential push-pull arrangement, the capacitive effects cancel each other out, eliminating the need for additional neutralization components and improving gain stability.
2Ease of operation
If passive switches are used for sign switching, then the switching function is achieved, but signal loss increases due to the switches being in the signal path
Solution Approach 1:
The invention replaces passive mechanical switches with an active electronic switching mechanism using two common-source amplifiers controlled in a push-pull manner. This substitution eliminates the need for switches to be directly in the signal path, as the amplifiers themselves perform the switching function through their controlled operation, thereby reducing signal loss.
3Reliability
If additional neutralization capacitors are added to compensate for gate-to-drain capacitance, then gain stability is improved, but the device complexity and parasitic effects increase
Solution Approach 1:
The invention makes the system self-service by using the inherent gate-to-drain capacitance of the amplifiers themselves to neutralize each other's capacitive effects. The two amplifiers in the push-pull configuration automatically compensate for capacitance without requiring external neutralization capacitors, thereby reducing component count and eliminating associated parasitic effects.
4Reliability
If the amplifiers are made asymmetric to optimize performance, then certain parameters are improved, but manufacturing precision and mismatch due to process variations worsen
Solution Approach 1:
The invention initially considers asymmetric amplifier design for performance optimization but ultimately adopts a symmetric push-pull configuration. The symmetry ensures that both amplifiers have identical characteristics, which minimizes mismatch due to process variations and simplifies manufacturing while still achieving performance goals through the differential operation.
Data Source
Figure 1A~1C
Figure 2
Figure 3~4
AI summary
Example embodiments describe a sign switching circuitry (100) comprising a first (191) and second (192) differential common-source amplifier having common differential input nodes (110, 121, 141, 111, 131, 151) and common differential output nodes (160, 123, 153, 161, 133, 143) configured such that a differential input signal applied at the common differential input nodes is amplified to a differential output signal at the common differential output nodes with a fixed gain by the first amplifier and by the fixed gain with opposite sign by the second amplifier; and a switching circuitry (170, 180) configured to activate the first common-source amplifier and deactivate the second common-source amplifier to amplify the differential input signal by the fixed gain, and to activate the second common-source amplifier and deactivate the first common-source amplifier to amplify the differential input signal by the fixed gain with opposite sign.