Phase Interpolator Circuit With Feedback for Low-Jitter CDR
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Solution Overview
Problem
Conventional phase selector/phase interpolator circuits in clock data recovery circuits introduce nonlinearity in output signals due to resistor loads, leading to increased clock jitter.
Innovation Solution
A phase selector/phase interpolator circuit with two phase selector circuits and one phase interpolator circuit, utilizing N first tail current tubes, phase selector units, a current source circuit, and a comparison circuit to ensure a linear triangular waveform and stable common-mode point, thereby reducing phase jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a resistor load is used in the phase selector circuit, then the circuit structure is simple, but the output waveform exhibits RC charging characteristics causing nonlinearity and phase interpolation errors
Solution Approach 1:
The patent changes the load type from resistor to current source, fundamentally altering the circuit's electrical characteristics. This parameter change transforms the output waveform from RC charging characteristics to linear triangular wave characteristics, eliminating nonlinearity while maintaining circuit simplicity
Solution Approach 2:
The patent introduces a feedback mechanism where the common-mode voltage is fed back to the tail current tube to dynamically adjust and stabilize the operating point. This feedback ensures that the current source maintains constant current output despite voltage variations, thereby eliminating nonlinearity and improving phase interpolation accuracy
2Adaptability or versatility
If the common-mode voltage fluctuates, then the circuit can operate with varying conditions, but the tail current changes causing nonlinearity and increased clock jitter
Solution Approach 1:
The patent employs feedback by connecting the common-mode voltage output to the tail current tube's control terminal. This feedback mechanism automatically adjusts the tail current to compensate for common-mode voltage fluctuations, maintaining constant current output and stable triangular wave generation across varying operating conditions
Solution Approach 2:
The circuit achieves self-regulation where the common-mode voltage automatically controls the tail current through the feedback connection. The system self-corrects for voltage fluctuations without external intervention, maintaining stable operation and linear waveform output across different operating conditions
Data Source
AI summary
A phase selector/phase interpolator circuit which includes two phase selector circuits and one phase interpolator circuit, each phase selector circuit includes N first tail current tubes, N phase selector units, a current source circuit and a comparison circuit. The current source circuit is selected as a load of the phase selector circuit. The comparison circuit compares a common-mode voltage of the two output clock signals output from the phase selector unit with a reference voltage, and performs negative feedback regulation on the first bias voltage of the first tail current tubes, so that the common-mode voltage can be controlled to be equal to the reference voltage, a tail current of the first tail current tubes is controlled to be equal to the current of the current source circuit, and the output waveform becomes a linear triangular wave.