MOSFET Switch Linearizing Circuit for Low Intermodulation Distortion
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Solution Overview
Problem
MOSFET switches in wireless communication circuits, such as direct-conversion radio receivers and transmitters, experience non-linear operation due to parasitic capacitances, leading to intermodulation distortion and performance issues.
Innovation Solution
A replica circuit with a reference resistance and operational amplifier is used to adjust the gate bias voltage of switching transistors, ensuring linear operation by replicating the switching element circuitry and matching the resistance, thereby mitigating non-linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MOSFET switches are used in direct-conversion radio receivers and transmitters, then switching function is achieved, but non-linear operation occurs due to parasitic capacitances causing intermodulation distortion
Solution Approach 1:
The patent applies feedback by sensing the source terminal voltage and applying it to the gate terminal through a feedback network. This feedback mechanism dynamically adjusts the gate voltage to compensate for non-linear effects caused by parasitic capacitances, thereby reducing intermodulation distortion and improving switching linearity throughout the signal cycle.
Solution Approach 2:
The patent changes the gate voltage parameter dynamically by applying the source terminal voltage to the gate terminal. This parameter change ensures that the gate-to-source voltage remains relatively constant during switching, which linearizes the switch resistance and reduces non-linear operation caused by parasitic capacitances.
2Reliability
If gate voltage is adjusted to close the switch, then low resistance is achieved, but non-linear resistance occurs due to charging times of capacitances
Solution Approach 1:
The patent dynamically changes the gate voltage parameter by applying the source terminal voltage to the gate terminal. This ensures that the gate-to-source voltage remains relatively constant during switching, which linearizes the switch resistance and reduces non-linear operation caused by parasitic capacitance charging times.
Solution Approach 2:
The feedback network senses the source terminal voltage and applies it to the gate terminal, creating a dynamic adjustment mechanism. This feedback ensures that the switch resistance remains linear throughout the switching transition, compensating for the non-linear effects of parasitic capacitance charging.
3Reliability
If larger voltage signals are employed in direct-conversion radio receivers and transmitters, then noise immunity is improved, but non-linear operation is exacerbated
Solution Approach 1:
The feedback mechanism senses the source terminal voltage and applies it to the gate terminal, dynamically compensating for non-linear effects. This allows the circuit to maintain linearity even when larger voltage signals are used for noise immunity, as the feedback continuously adjusts the gate voltage to counteract non-linear distortion.
Solution Approach 2:
By dynamically changing the gate voltage parameter to follow the source terminal voltage, the patent maintains constant gate-to-source voltage during switching. This parameter adjustment ensures that larger signal voltages do not push the switch into non-linear operation, thereby preventing intermodulation distortion while preserving noise immunity.
Data Source
AI summary
A transistor-based switch is coupled to a replica circuit that includes transistor circuitry similar to that of the switch. The replica circuit biases a switched transistor to promote linear operation of the switch.