Integrator Circuit Output Resistance Control for PVT Phase Stability
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Solution Overview
Problem
Existing analog mixed-signal integrated circuits with continuous-time filters based on elementary integrator cells face challenges due to PVT-induced fluctuations, which affect the phase shift and frequency response, especially at high frequencies and over wide frequency ranges.
Innovation Solution
The output resistance of the input transconductance amplifier is made adjustable through a dedicated control signal, with a matched transconductance amplifier and a second control loop that adjusts resistances to maintain constant voltage, ensuring phase stability across PVT variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the transconductance gain Gi is fixed over a large range of values, then the integrator can operate at different frequencies, but the phase shift becomes PVT-dependent and deviates from ideal 90°
Solution Approach 1:
The patent makes the output resistance Ri dynamically adjustable through a dedicated control signal Vc, allowing it to vary independently from the transconductance gain Gi. This dynamic adjustment compensates for PVT variations and maintains constant phase shift of 90° across the full frequency tuning range, resolving the contradiction between frequency adaptability and phase stability
Solution Approach 2:
The patent changes the resistance parameter Ri independently from the transconductance gain by introducing a separate control voltage Vc that adjusts the output resistance of both transconductance amplifiers Gi and Gi2. This parameter change allows the system to maintain ideal integrator characteristics (90° phase shift) while operating over a wide frequency range, resolving the contradiction between frequency tuning and phase stability
2Device complexity
If the output resistance Ri is fixed, then the circuit is simple, but the voltage gain (Gi Ri) and phase response are affected by PVT fluctuations
Solution Approach 1:
The patent implements a feedback mechanism where the output of matched transconductance amplifier Gi2 is fed back through error amplifier Avo to control the output resistance of both Gi and Gi2 via control voltage Vc. This feedback loop compensates for PVT variations in real-time, maintaining stable voltage gain and phase response without significantly increasing circuit complexity
Solution Approach 2:
The patent introduces a controllable parameter change in the output resistance Ri through control voltage Vc, allowing the resistance to adapt to PVT conditions. This is achieved by adjusting the operating point of the output transistors, thereby changing their effective resistance to compensate for PVT drift and maintain reliable operation
3Speed
If the transconductance amplifier operates at high frequencies, then the filter performance is improved, but the phase shift deviates from 90° due to PVT variations
Solution Approach 1:
The patent dynamically adjusts the output resistance Ri at high frequencies through control voltage Vc to compensate for frequency-dependent PVT variations. This dynamic adjustment ensures that the phase shift remains accurately at 90° even when operating at high frequencies where PVT effects are more pronounced, resolving the contradiction between speed and phase accuracy
Data Source
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AI summary
An architecture of an integrator has an input transconductance amplifier Gi having an output resistance adjustable independently from the transconductance gain Gi, through a dedicated control signal, and includes also a matched transconductance amplifier Gi2 having an adjustable gain and an output resistance matched with that of the first transconductance amplifier Gi and adjusted by the same dedicated control signal. A reference current is forced through the matched output resistance and the dedicated control signal is generated such to keep constant the output voltage of the matched transconductance amplifier. A method of stabilization against PVT variations of the integrated circuit of an integrator is also disclosed.