Receiver Equalization Circuit for Baseline Wander and DC Level Shift
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Solution Overview
Problem
Baseline wander in AC coupled serializer/deserializer links leads to low-frequency noise, particularly harmful for multi-level signaling, as existing feedback correction mechanisms introduce delays and impairments, making them imperfect.
Innovation Solution
A receiver circuit configuration that includes a resistor and capacitor in parallel, coupled with current sources adjusted by a common mode feedback op-amp, which acts as a linear equalizer and performs DC level shifting to prevent baseline wander and achieve linear equalization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a feedback mechanism is used to correct baseline wander, then baseline wander correction is achieved, but delay is introduced and correction imperfection remains
Solution Approach 1:
The patent applies preliminary action by proactively preventing baseline wander through a feed-forward equalizer that processes signals before they accumulate DC offset, rather than reacting to it afterward. The circuit continuously monitors and adjusts the common-mode voltage level in real-time, eliminating the need for delayed feedback correction and avoiding the associated time loss and imperfections.
2Device complexity
If AC coupling capacitor is placed on semiconductor die, then integration is improved, but baseline wander correction capability deteriorates
Solution Approach 1:
The patent merges the AC coupling function with a common-mode feedback equalization circuit directly on the semiconductor die. By integrating both the AC capacitor and the active equalization mechanism (comprising operational amplifiers, resistors, and capacitors) into a unified circuit block, the design achieves both compact integration and effective baseline wander correction without requiring external components.
3Reliability
If feedback mechanism is used for baseline wander correction, then correction is achieved, but link budget impairment increases
Solution Approach 1:
The patent replaces the conventional feedback-based mechanical correction system with an active electronic equalization circuit that uses operational amplifiers to generate compensating signals. This substitution eliminates the need for high-gain feedback loops and associated noise amplification, thereby reducing link budget impairment while maintaining effective baseline wander correction.
Data Source
AI summary
Systems, apparatuses, and methods for implementing a combo scheme for direct current (DC) level shifting of signals are disclosed. A receiver circuit receives an input signal on a first interface. The first interface is coupled to a resistor in parallel with a capacitor which passes the input signal to a second interface. Also, the first interface is coupled to a first pair of current sources between ground and a voltage source, and the second interface is coupled to a second pair of current sources between ground and the voltage source. An op-amp drives the current sources based on a difference between a sensed common mode voltage and a reference voltage. Based on this circuit configuration, the receiver circuit is able to prevent baseline wander, perform a DC level shift of the input signal, and achieve linear equalization of the input signal.