Auxiliary Compensation Circuit for Low-Power Amplifier Phase Margin
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Solution Overview
Problem
Audio amplifiers used in loudspeakers can become unstable due to the Zobel network when in low power mode, particularly due to reduced bias current and loop gain, leading to phase dips and gain droop.
Innovation Solution
A multi-stage amplifier with a compensation circuit comprising auxiliary amplifiers, capacitors, and resistors is introduced to provide a zero at low frequency, compensating for phase dips and stabilizing the system by increasing phase margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If bias current and loop gain of output amplifier stage are reduced for low power mode, then power consumption is reduced, but amplifier stability deteriorates due to phase dip from Zobel network
Solution Approach 1:
The patent introduces a compensation circuit as an intermediary component between the amplifier stages. This circuit includes a first auxiliary amplifier with a capacitor coupled between its input and output terminals, a second auxiliary amplifier, and resistors that create a positive phase trapezoid at low frequencies to counteract the phase dip caused by the Zobel network, thereby maintaining stability while operating in low-power mode
Solution Approach 2:
The compensation circuit dynamically adjusts the phase response parameters of the amplifier system. By introducing additional poles and zeros through the auxiliary amplifiers and capacitors, the circuit modifies the frequency response characteristics to provide phase boost at critical frequencies where the Zobel network causes instability, enabling stable operation across different power modes
2Reliability
If Zobel network is added to damp high-frequency oscillations, then high-frequency stability is improved, but phase margin is reduced causing amplifier instability in low power mode
Solution Approach 1:
The patent converts the harmful phase dip effect of the Zobel network into a beneficial configuration by introducing a compensation circuit that creates an equal but opposite phase effect. The positive phase trapezoid generated by the auxiliary amplifiers and capacitors precisely counterbalances the negative phase contribution from the Zobel network, transforming the stability problem into a solved condition
Solution Approach 2:
The compensation circuit applies preliminary counter-action to the phase dip caused by the Zobel network. By placing the compensation circuit in the signal path before the instability manifests, the circuit pre-compensates for the phase loss, ensuring that the total phase shift remains within stable operating limits even when the amplifier operates in low-power mode with reduced bias current
Data Source
AI summary
The present invention provides a multi-stage amplifier, wherein the multi-stage amplifier includes a plurality of amplifier stages and a compensation circuit. The compensation circuit is coupled to an output terminal of one of the plurality of amplifier stages, and the compensation circuit includes a first auxiliary amplifier, a capacitor, a second auxiliary amplifier, a first resistor and a second resistor. The capacitor is coupled between an input terminal and an output terminal of the first auxiliary amplifier. The second auxiliary amplifier is coupled to the first auxiliary amplifier. The first resistor is coupled between an input terminal and an output terminal of the second auxiliary amplifier. The second resistor is coupled between an output terminal of the first auxiliary amplifier and a ground voltage.