Signal Amplifier Power Rejection Circuit for Linear-Region Noise
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Solution Overview
Problem
Conventional signal amplifier circuits with high power supply rejection ratio (PSRR) face issues such as low noise rejection bandwidth, high power consumption, asymmetrical transient responses, and inability to reject noises when operating in the linear region, relying on external output capacitor for loop stability.
Innovation Solution
A signal amplifier circuit design incorporating a pre-amplifier circuit, a driver circuit with a driving transistor, and a power rejection circuit that includes a noise selection circuit and unilateral control circuits to generate a power rejection signal, effectively rejecting AC components of power noise and improving PSRR by operating within specific operation regions and using feed-forward compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a common source structure is used in the differential forward noise cancellation circuit, then the circuit can reject noise, but the bandwidth of noise rejection is relatively low and power consumption increases
Solution Approach 1:
The power rejection circuit is divided into multiple parallel unilateral control circuits, each handling specific frequency ranges or noise components. This segmentation allows broader noise rejection bandwidth while distributing power consumption across multiple simpler stages rather than one complex common source circuit
Solution Approach 2:
The circuit dynamically switches between different operation modes (common source configuration and unilateral control configuration) based on the operating conditions and noise characteristics. This dynamic adaptation allows the circuit to achieve broad noise rejection bandwidth while optimizing power consumption for different operating scenarios
2Reliability
If a current mirror is used in the driver circuit output stage, then the circuit can provide stable current, but the rising and falling of driving signal cause asymmetrical transient responses
Solution Approach 1:
The patent intentionally introduces asymmetrical compensation elements that counterbalance the inherent asymmetry of the current mirror. By adding compensating capacitance or resistance elements with opposite polarity characteristics, the overall transient response becomes symmetrical while maintaining the current stability benefit of the current mirror structure
3Power
If the driving transistor operates in linear region, then the circuit can provide high current, but the circuit cannot reject undesirable noises
Solution Approach 1:
The circuit dynamically adjusts the operating region of the driving transistor based on the type of noise present. When linear region operation is required for high current, the unilateral control circuits are activated to provide noise rejection. This dynamic switching allows the circuit to simultaneously achieve high current output and noise rejection by coordinating the transistor operation mode with the active compensation mechanism
4Reliability
If external output capacitor is used for loop stability, then the circuit can maintain stability, but the circuit cannot perform internal feed-forward compensation
Solution Approach 1:
The circuit incorporates internal feed-forward compensation mechanisms that operate autonomously within the amplifier itself, eliminating dependence on external capacitor characteristics for stability. The unilateral control circuits provide self-contained compensation that actively counteracts instability sources, allowing the circuit to maintain loop stability while achieving broad noise rejection and improved transient response without requiring specific external capacitor values
Data Source
AI summary
A signal amplifier circuit having high power supply rejection ratio includes: a pre-amplifier which generates a driving signal at a driving control node; and a driving circuit which converts an input power to an output power. The driving circuit includes: a driving transistor, having a first terminal coupled to the input power and a second terminal coupled to the output power; and a power rejection circuit which includes a noise selection circuit. When the driving transistor operates in its linear region, the power rejection circuit senses an AC component of a power noise of the input power to generate an operation noise signal. The power rejection circuit generates the power rejection signal in AC form according to the operation noise signal to reject the power noise so as to increase the power supply rejection ratio.