CDR Charge Pump Compensation for Low Charge Sharing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The charge sharing effect in clock and data recovery (CDR) circuits, caused by impedance mismatch between the input and output channels of the charge pump (CP) circuit, leads to an imbalance in the control voltage, degrading the performance of the CDR circuit.
Innovation Solution
A CDR circuit is designed with a low pass filter (LPF) and a CP circuit that includes operational amplifiers, switch circuits, and compensation resistors to achieve an ultra-low charge sharing effect. The compensation resistors are added to balance the precharging and output channels, while degeneration resistors are used to reduce the influence of mismatches in the switch circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a charge pump circuit is used to convert up signals and down signals into control voltage, then the frequency of the clock signal can be controlled and adjusted, but impedance mismatch between input and output channels causes charge sharing effect that degrades circuit performance
Solution Approach 1:
The charge pump circuit is segmented into separate precharging channel and output channel, each with dedicated compensation resistors. This segmentation allows independent optimization of each channel's impedance characteristics to eliminate charge sharing effects between channels.
Solution Approach 2:
Different compensation resistors are applied to different parts of the circuit (precharging channel vs output channel) based on their specific impedance requirements. The first compensation resistor is coupled to the first high-side switch circuit, and the second compensation resistor is coupled to the first low-side switch circuit, providing localized impedance matching.
2Measurement precision
If compensation resistors are added to balance precharging and output channels, then charge sharing effect is minimized and control voltage accuracy is improved, but device complexity increases
Solution Approach 1:
The values of compensation resistors are carefully selected and adjusted to match the impedance characteristics of different channels. By changing the resistance parameters to specific optimal values, the charge sharing effect is minimized without requiring complex additional circuitry.
3Stability of the object's composition
If degeneration resistors are used to reduce the influence of switch circuit mismatches, then loop balance is improved, but device complexity increases
Solution Approach 1:
Degeneration resistors are incorporated into the switch circuits in advance to preemptively compensate for potential mismatches. This preliminary action prevents loop balance issues before they occur, rather than requiring complex feedback correction mechanisms.
Data Source
AI summary
A clock and data recovery (CDR) circuit includes a low pass filter (LPF) and a charge pump (CP) circuit. The LPF includes a filtering resistor and a filtering capacitor. The CP circuit, coupled to the LPF, includes an operational amplifier, a first high-side switch circuit, a first low-side switch circuit, a second high-side switch circuit, a second low-side switch circuit, a first compensation resistor and a second compensation resistor. The first high-side switch circuit and the first low-side switch circuit are coupled to an output terminal of the operational amplifier. The second high-side switch circuit and the second low-side switch circuit are coupled to a first input terminal of the operational amplifier through the LPF. The first compensation resistor is coupled to the first high-side switch circuit. The second compensation resistor is coupled to the first low-side switch circuit.