Programmable Gain Amplifier Circuit for MOSFET Leakage Cancellation
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Solution Overview
Problem
Programmable gain amplifiers face challenges in maintaining accurate gain values due to temperature-dependent current leakage from MOSFET switches, leading to non-linearity and gain errors.
Innovation Solution
Incorporating a switch leakage compensation circuit with a compensation transconductance amplifier and a switchable compensation resistance network, where gain-mimicking switches operate complementary to gain-setting switches, to cancel out leakage currents and improve linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If MOSFET switches are used in the switchable resistance network to set gain values, then the programmable gain amplifier can achieve multiple gain settings, but temperature-dependent current leakage from the MOSFET switches causes non-linearity and gain errors
Solution Approach 1:
The patent converts the harmful leakage current from MOSFET switches into a beneficial compensation signal. By intentionally generating an equal and opposite leakage current through the compensation transconductance amplifier, the harmful effect of switch leakage is transformed into a corrective mechanism that eliminates gain errors and non-linearity, thereby improving gain accuracy while maintaining multi-gain capability
Solution Approach 2:
The patent implements a feedback mechanism where the compensation transconductance amplifier continuously monitors and counteracts the leakage current from the main transconductance amplifier's switches. The compensation circuit uses the same switch control signals to generate compensating currents that feed back into the output, dynamically correcting for leakage effects across different gain settings and temperatures
2Adaptability or versatility
If a switchable resistance network with multiple branches is used to provide programmable gain, then various gain values can be selected, but the leakage current from switches degrades linearity
Solution Approach 1:
The patent converts the harmful non-linear leakage current into a beneficial compensation mechanism. The compensation transconductance amplifier generates leakage currents that are equal in magnitude but opposite in polarity to the harmful leakage from the main amplifier's switches, thereby transforming the non-linear distortion into a linearizing effect that maintains signal integrity across all gain settings
Solution Approach 2:
The patent dynamically changes the compensation parameters by using the same switch control signals to configure both the main and compensation transconductance amplifiers. This ensures that the compensation circuit's characteristics match the main amplifier's switch configuration at any given moment, maintaining optimal linearity compensation across the full range of programmable gain values
Data Source
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AI summary
A programmable gain amplifier (200) that comprises: a transconductance amplifier (201), a switch leakage compensation circuit (210) and a transimpedance amplifier (202). The transconductance amplifier (201) provides a transconductance amplifier current signal and includes a switchable resistance network. The switch leakage compensation circuit (210) provides a compensation current signal and comprises a switchable compensation resistance network. The transimpedance amplifier (202) provides the output voltage signal based on the difference between the transconductance amplifier current signal and the compensation current signal. The switchable compensation resistance network comprises a plurality of branches in parallel with each other, wherein each branch includes: a gain-mimicking switch that has a corresponding gain-setting switch in the switchable resistance network; and a leakage-current-conducting switch in series with the gain-mimicking switch. The leakage-current-conducting switch is openable and closable in accordance with the complement of a switch control signal that is used to control the gain-mimicking switch in the same branch.