Variable-Gain Linear Equalizer With Diode-Connected Load Boost
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Solution Overview
Problem
Conventional equalizers for high-speed data transmission suffer from excessive die space requirements, low DC gain, limited output voltage swing, and high power consumption, which are not suitable for modern microprocessors processing wide-bit words due to issues like bit error rates and channel distortion on wide-bit buses.
Innovation Solution
A linear equalizer design featuring diode-connected load transistors with adaptive impedance, where capacitors control the diode connection based on the instantaneous frequency of the differential input signal, allowing for increased high-frequency gain without excessive power consumption or die area demands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional equalizers are used to boost high-frequency components, then channel distortion is compensated, but die space requirement increases excessively
Solution Approach 1:
The patent changes the impedance parameter of the load transistor dynamically by controlling its gate voltage. By switching between diode-connected configuration (low impedance) and non-diode-connected configuration (high impedance), the equalizer achieves frequency-dependent gain adjustment without requiring additional circuit components, thereby reducing die space while maintaining distortion compensation capability
Solution Approach 2:
The patent introduces dynamic control of the load transistor configuration based on the instantaneous frequency of the input signal. A frequency detection mechanism dynamically switches the load transistor between diode-connected and non-diode-connected states, enabling adaptive equalization that responds to signal characteristics in real-time, thus achieving effective distortion compensation with reduced hardware overhead
2Reliability
If conventional equalizers are used to boost high-frequency components, then channel distortion is compensated, but power consumption increases excessively
Solution Approach 1:
The patent employs periodic switching of the load transistor configuration synchronized with the signal frequency characteristics. By activating the high-gain non-diode-connected mode only when high-frequency components are detected (rather than continuously), the equalizer reduces average power consumption while maintaining distortion compensation during critical signal periods
Solution Approach 2:
The patent dynamically adjusts the operating parameter (impedance) of the load transistor based on signal frequency content. This parameter change enables the circuit to operate in low-power diode-connected mode during normal conditions and switch to high-performance non-diode-connected mode only when needed for distortion compensation, optimizing the power-performance tradeoff
3Reliability
If conventional equalizers are used to boost high-frequency components, then channel distortion is compensated, but DC gain becomes insufficient
Solution Approach 1:
The patent implements dynamic configuration switching of the load transistor that responds to the instantaneous frequency of the input signal. When high-frequency components are detected, the circuit dynamically transitions to the non-diode-connected configuration which provides high-frequency gain boost, while maintaining adequate DC gain during low-frequency operation through the diode-connected configuration
Solution Approach 2:
The patent applies different impedance characteristics to the load transistor based on the local frequency content of the signal. The diode-connected configuration provides appropriate gain for low-frequency/DC components, while the non-diode-connected configuration provides enhanced gain for high-frequency components, achieving frequency-selective equalization that addresses both DC gain and high-frequency distortion compensation requirements
4Reliability
If conventional equalizers are used to boost high-frequency components, then channel distortion is compensated, but output voltage swing becomes limited
Solution Approach 1:
The patent dynamically switches the load transistor configuration based on signal frequency, enabling the circuit to maintain high output voltage swing during low-frequency operation (diode-connected mode) and provide frequency-dependent gain enhancement during high-frequency operation (non-diode-connected mode), thus achieving distortion compensation without permanently limiting voltage swing
Solution Approach 2:
The patent changes the load transistor's impedance parameter dynamically to match signal frequency characteristics. This parameter change allows the circuit to optimize between output swing and gain enhancement at different frequencies, maintaining adequate voltage swing headroom while providing necessary high-frequency boost when required
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A linear equalizer is configured with load transistors that load a corresponding differential pair of transistors. The linear equalizer is configured to selectively diode connect each load transistor to boost a high frequency gain.