Integrator Circuit Phase Stabilization Across PVT Variations
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Solution Overview
Problem
Analog mixed-signal integrated circuits with continuous-time filters based on elementary integrator cells face phase shifts due to process spread, supply voltage, and temperature fluctuations, affecting their frequency response, especially at high frequencies and wide tunable ranges.
Innovation Solution
The output resistance of the input transconductance amplifier is made independently adjustable through a dedicated control signal, with a matched transconductance amplifier and a second control loop that adjusts resistances to maintain a constant output voltage, stabilizing the phase of the integrator cell against PVT variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the transconductance gain Gi is fixed in a large range of values, then the integrator can operate at different frequencies, but the phase of the transfer function becomes PVT-dependent and deviates from 90°
Solution Approach 1:
The patent applies dynamics by making the output resistance Ri independently adjustable through a dedicated control signal Vc, allowing the system to adapt its parameters dynamically. The adjustable resistive element Ri (implemented via controlled resistors) enables real-time modification of the integrator's characteristics to maintain phase stability across different operating conditions while preserving frequency tuning capability through the Gi-Ci configuration.
2Device complexity
If the output resistance Ri is fixed, then the circuit structure is simple, but the phase response becomes sensitive to PVT variations
Solution Approach 1:
The patent implements parameter changes by introducing a dedicated control signal Vc that independently adjusts the output resistance Ri through an adjustable resistive element. This allows the resistance parameter to be modified without changing the fundamental Gi-Ci integrator structure, thereby maintaining circuit simplicity while improving phase response stability against PVT variations through dynamic parameter adaptation.
3Stability of the object's composition
If a matched transconductance amplifier Gmi and control loop are added to compensate PVT fluctuations, then phase stability is improved, but the device complexity increases
Solution Approach 1:
The patent applies feedback through a control loop that uses the matched transconductance amplifier Gmi to sense and compensate for PVT-induced variations. The error amplifier Aio compares the reference current from the DAC with the current Gmi*Vr and adjusts the gain of Gi and Gmi to nullify differences, while the dedicated control signal Vc adjusts Ri to maintain phase stability. This feedback mechanism improves phase stability while keeping the complexity manageable through efficient use of matched components.
Data Source
AI summary
An integrated circuit integrator includes a first transconductance amplifier having a gain adjustable based upon a first control signal, and receives, as an input, a signal to be filtered, and generates, as an output, a corresponding amplified signal. The first transconductance amplifier includes an R-C output circuit to filter components from the amplified signal, and an output resistance being adjustable based upon a second control signal. A second transconductance amplifier is matched with the first transconductance amplifier, and has a gain adjustable based upon the first control signal, and a matched output resistance adjustable based upon the second control signal. A circuit is configured to force a reference current through the matched output resistance. An error correction circuit is coupled to the second transconductance amplifier and is configured to generate the second control signal so as to keep constant a voltage on an output of the second transconductance amplifier.