Cancellation Capacitor Switching for Mixer-Induced Distortion
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Solution Overview
Problem
Zero IF receivers face issues with 1/f flicker noise in the baseband signal chain and distortion caused by transimpedance amplifiers, which worsen with increasing frequency due to switched capacitance equivalent resistance of mixer switches.
Innovation Solution
The implementation of a circuit with operational amplifiers, mixer switches, and cancellation capacitors that switch input nodes between the operational amplifier's positive and negative inputs based on clock signals, using cancellation capacitors to neutralize the charge on parasitic capacitances, thereby reducing noise and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If mixer switches are used to switch input nodes between operational amplifier inputs, then signal routing flexibility is improved, but distortion increases due to switched capacitance equivalent resistance
Solution Approach 1:
The patent introduces cancellation capacitors as intermediary elements between the mixer switches and the operational amplifier inputs. These capacitors act as mediators that cancel out the harmful switched capacitance effects. The cancellation capacitors are controlled by clock signals to switch between connected and disconnected states, actively compensating for the distortion caused by the mixer switches' equivalent resistance.
2Power
If transimpedance amplifiers are used in the baseband signal chain, then signal amplification is improved, but 1/f flicker noise is generated
Solution Approach 1:
The patent extracts and removes the harmful 1/f flicker noise component from the baseband signal chain. By using cancellation capacitors that are switched in synchronization with the mixer clock signals, the circuit actively extracts and cancels the noise generated by the transimpedance amplifiers, allowing the amplifiers to maintain their signal amplification function while eliminating their harmful noise output.
3Object-generated harmful factors
If cancellation capacitors are added to neutralize parasitic capacitance charge, then noise and distortion are reduced, but device complexity increases
Solution Approach 1:
The patent merges the cancellation capacitor functionality with the existing mixer switch infrastructure. The cancellation capacitors are integrated into the same clock signal distribution network and switch control mechanism already present in the mixer circuit. This merging approach allows the noise cancellation function to be added without requiring completely separate control logic or timing circuits, thereby limiting the increase in device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces noise and distortion by ensuring a net zero charge at the input nodes, minimizing the impact of parasitic capacitances on the operational amplifiers and improving the overall performance of the receiver.
Implementation Method 1
A cancellation capacitor is coupled to the first input node. A third switch selectively couples the cancellation capacitor to the first internal node of the operational amplifier. A fourth switch selectively couples the cancellation capacitor to the second internal node of the operational amplifier.
Data Source
AI summary
A circuit includes first and second operational amplifiers, each including positive and negative inputs and first and second internal nodes. A mixer couples first and second input nodes to the positive and negative inputs of the operational amplifiers. The mixer switches the first and second input nodes between the positive and negative inputs of the first and second operational amplifiers in accordance with clock signals. A first cancellation capacitor couples to the first input node, and a second cancellation capacitor couple to the second input node. First and second switches selectively couple the first cancellation capacitor to the first and second internal nodes, respectively, of the first operational amplifier. Third and fourth switches selectively couple the second cancellation capacitor to the first and second internal nodes, respectively, of the second operational amplifier.