Two-Stage Circuit RC Noise Mirroring for Power Supply Rejection
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Solution Overview
Problem
Two-stage circuits, such as amplifiers and low-dropout regulators, suffer from power supply noise rejection issues due to mid-range frequency noise coupling through RC compensation circuits, leading to undesirable amplification of power supply noise in output voltages, which affects the fidelity of components like voltage-controlled oscillators and low-noise amplifiers.
Innovation Solution
Incorporating a resistor-capacitor (RC) circuit between the drain of a diode-connected transistor and ground in the first stage of a two-stage circuit, which conducts noise currents and mirrors them through a current mirror to oppose noise currents in the output transistor, reducing the overall noise impact by acting as a power supply rejection filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If an RC compensation circuit is used in the second stage, then stability is improved, but power supply noise is amplified at mid-range frequencies
Solution Approach 1:
The invention divides the noise filtering function into two separate RC circuits: one in the first stage (RC filter) and one in the second stage (RC compensation circuit). This segmentation allows each circuit to handle different aspects of noise rejection while maintaining overall stability, with the first stage RC circuit specifically targeting mid-range frequency noise before it reaches the second stage.
Solution Approach 2:
The first stage RC circuit acts as an intermediary noise filtering element between the power supply and the second stage. It pre-filters power supply noise at mid-range frequencies before the signal enters the second stage, reducing the noise burden on the RC compensation circuit while maintaining stability.
2Reliability
If noise filtering is enhanced, then power supply rejection is improved, but circuit complexity increases
Solution Approach 1:
The first stage RC circuit serves multiple functions: it acts as a power supply noise filter for mid-range frequencies, provides biasing for the differential pair, and contributes to overall circuit compensation. This multi-functionality achieves enhanced power supply rejection without proportionally increasing circuit complexity.
Solution Approach 2:
The invention optimizes the RC time constant of the first stage RC circuit to specifically target mid-range frequency noise (typically 100 kHz to 10 MHz). By carefully selecting R and C values, the circuit achieves effective noise rejection at critical frequencies while maintaining proper biasing and stability conditions.
Data Source
AI summary
A two-stage circuit includes a differential-to-single-ended first stage with a differential pair of transistors. The first stage includes a current mirror including a diode-connected transistor having an RC circuit coupled to a drain of the diode-connected transistor. The current mirror is configured to mirror a power supply noise current conducted by the RC circuit through a first stage output terminal to a gate of an output transistor in a second stage of the two-stage circuit.