LDO Ripple Cancellation Circuit for Supply Noise-Sensitive SerDes
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Solution Overview
Problem
Modular units in integrated circuit designs, such as high bandwidth serializer/deserializer modules, are sensitive to power supply noise, which increases jitter and affects performance, and existing noise reduction techniques are complex, power-hungry, or impractical for use in predefined modular units.
Innovation Solution
A low drop out (LDO) voltage regulator circuit with a pass transistor, operational amplifier, buffer, and coupling capacitor is used to derive and impose a ripple cancellation signal, reducing power supply noise through capacitive coupling, thereby improving the power supply rejection ratio and reducing jitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If existing power supply noise reduction techniques are used, then power supply noise is reduced, but device complexity increases
Solution Approach 1:
A buffer circuit is introduced as an intermediary component between the power supply and the SerDes module. The buffer derives a ripple cancellation signal from the power supply voltage and couples it through a coupling capacitor to cancel power supply noise, thereby reducing complexity compared to more sophisticated noise reduction techniques while maintaining effectiveness
Solution Approach 2:
The power supply noise reduction function is extracted as a separate buffer circuit with a coupling capacitor, independent from the main SerDes module. This allows the noise reduction functionality to be implemented without complicating the core SerDes design, addressing the contradiction by separating concerns
2Object-affected harmful factors
If existing power supply noise reduction techniques are used, then power supply noise is reduced, but power consumption increases
Solution Approach 1:
The buffer acts as a low-power intermediary that derives the ripple cancellation signal from the existing power supply voltage without requiring additional power-consuming noise reduction circuits. The coupling capacitor further reduces power consumption by blocking DC components while allowing AC noise cancellation signals to pass
Solution Approach 2:
The buffer circuit uses the power supply voltage itself to generate the ripple cancellation signal, rather than requiring separate power-consuming active noise reduction circuits. The circuit essentially uses the power supply's own characteristics to cancel its own noise
3Stability of the object's composition
If power supply noise is reduced, then jitter is reduced, but device complexity increases
Solution Approach 1:
The buffer and coupling capacitor serve as simple intermediary components that reduce jitter by canceling power supply noise without introducing complex jitter correction circuits. The solution addresses jitter at its source (power supply noise) rather than requiring complex downstream signal processing
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces power supply noise, improving the power supply rejection ratio and bit error rates in SerDes modules, while simplifying the circuit and reducing complexity and power consumption.
Implementation Method 1
a coupling capacitor that couples the buffer to the base or gate of the pass transistor to impose the ripple cancellation signal on the control signal
Data Source
AI summary
Power supply noise reduction methods and low drop out (LDO) voltage regulators with capacitively coupled supply noise-reducing components are disclosed. One illustrative voltage regulator includes: a pass transistor having an n-type conduction channel that couples a supply voltage to an output node; an operational amplifier that derives a control signal for the pass transistor from a difference between a reference voltage and a scaled or unscaled voltage of the output node, the control signal being supplied to a gate or base of the pass transistor; a buffer that derives a ripple cancellation signal from the supply voltage; and a coupling capacitor that couples the buffer to the base or gate of the pass transistor to impose the ripple cancellation signal on the control signal.