Chopper amplifying circuit employing negative impedance compensation technique
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Solution Overview
Problem
Chopper amplifying circuits in prior art struggle to achieve extremely high input impedance while maintaining stability, limiting their applicability in scenarios requiring high input impedance for low-noise amplification of weak signals.
Innovation Solution
The introduction of a negative impedance compensation technique using a negative impedance converting circuit parallel-connected to the signal input end of the first-level amplifying circuit, reducing equivalent input capacitance and increasing input impedance without introducing positive feedback, which can destabilize the circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If positive feedback loop is introduced to increase input impedance, then input impedance is improved, but circuit stability deteriorates
Solution Approach 1:
The patent applies negative feedback instead of positive feedback to achieve the desired effect. By inverting the feedback polarity, the circuit achieves input impedance enhancement while maintaining stability. The negative feedback loop compensates for the capacitive effect by introducing an opposing signal that reduces the net capacitive reactance at the input terminal.
Solution Approach 2:
The patent changes the feedback parameter from positive to negative to resolve the contradiction. By adjusting the feedback polarity and magnitude, the circuit achieves both high input impedance and stability. The feedback factor and impedance values are optimized to achieve the desired input impedance while keeping the circuit stable.
2Shape
If input capacitance is reduced to increase input impedance, then input impedance is improved, but amplification precision deteriorates due to parasitic parameters
Solution Approach 1:
The patent introduces a feedback network as an intermediary mechanism to achieve input impedance enhancement without directly reducing input capacitance. The feedback network acts as a mediator that compensates for the capacitive effect through impedance transformation, thereby maintaining both high input impedance and amplification precision by avoiding direct manipulation of the input capacitor values.
3Shape
If positive feedback is excessively introduced to achieve extremely high input impedance, then input impedance is improved, but circuit stability severely deteriorates
Solution Approach 1:
The patent fundamentally inverts the approach by using negative feedback instead of positive feedback. This inversion allows the circuit to achieve extremely high input impedance (above GΩ) while maintaining stability. The negative feedback mechanism provides a stabilizing effect that prevents oscillation and ensures reliable operation even at very high impedance levels.
Solution Approach 2:
The patent employs a carefully designed negative feedback loop that provides stable operation. The feedback network is configured with specific impedance values and topology to achieve the desired input impedance enhancement while maintaining circuit stability. The feedback factor is optimized to provide sufficient impedance transformation without causing instability or oscillation.
Data Source
AI summary
A chopper amplifying circuit employing a negative impedance compensation technique, including a differential input end, a first-level chopper switch, a first-level amplifying circuit, a second-level chopper switch, a second-level amplifying circuit, a negative impedance converting circuit, a negative feedback unit, an input capacitor, and a differential output end, is provided. The differential input end is connected to the first-level chopper switch. An output terminal of the first-level chopper switch is connected to the first-level amplifying circuit through the input capacitor. The first-level amplifying circuit is connected to the second-level chopper switch, which is connected to the second-level amplifying circuit. The second-level amplifying circuit is connected to the differential output end, and is also connected to a feedback input end of the first-level amplifying circuit through the negative feedback unit. The negative impedance converting circuit is parallel-connected to a signal input end of the first-level amplifying circuit.