LVDS Receiver Feedback Circuit for Wide Common-Mode Range
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Solution Overview
Problem
Existing LVDS receiver circuits face challenges in achieving sufficient voltage gain, converting differential to single output voltage, maintaining high switching speed, and operating within wide input and supply voltage ranges while being robust against process variations without requiring special transistors or bias voltages.
Innovation Solution
The LVDS receiver circuit employs a differential-input transistor pair, current-mirror-load circuit, and feedback inverters to provide voltage gain and convert differential input voltage to single output voltage, utilizing a simple structure that includes negative feedback loops to stabilize voltage and improve switching speed without needing special processes or bias voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a complex amplifier circuit is used to achieve large voltage gain and wide common-mode range, then voltage gain and adaptability are improved, but device complexity increases and switching speed decreases
Solution Approach 1:
The inverter circuit performs multiple functions simultaneously: it provides voltage gain through its amplification capability, converts differential signals to single-ended output, and operates across a wide common-mode voltage range (0.3V to 2.5V). This multi-functionality eliminates the need for separate circuits for each function, reducing overall complexity while maintaining adaptability.
Solution Approach 2:
The inverter uses its own output signal to control its input transistors through feedback, creating a self-regulating system. The output voltage directly influences the gate voltages of the input transistors, allowing the circuit to automatically adjust its operation across different common-mode voltage ranges without requiring external control circuits.
2Adaptability or versatility
If a complex amplifier circuit is used to achieve large voltage gain, then voltage gain is improved, but device complexity increases
Solution Approach 1:
The inverter circuit provides voltage gain as one of its inherent functions while simultaneously performing differential-to-single-ended conversion. The gain is achieved through the transconductance of the input transistors and the loading effect of the subsequent inverter stage, eliminating the need for a separate gain stage.
Solution Approach 2:
The circuit employs feedback where the output voltage is fed back to control the gate voltages of the input transistors. This feedback mechanism enhances the voltage gain by creating a regenerative effect that amplifies the differential input signal while maintaining stability across wide voltage ranges.
3Adaptability or versatility
If additional bias voltage is added to achieve wide input voltage range, then adaptability is improved, but device complexity increases
Solution Approach 1:
The inverter circuit automatically adapts to different input voltage ranges using its own output signal for control. The feedback mechanism allows the circuit to self-regulate its operating point across a wide common-mode voltage range (0.3V to 2.5V) without requiring external bias voltages or reference signals, thereby maintaining adaptability while minimizing complexity.
4Speed
If amplifier circuit is simplified to enhance switching speed, then switching speed is improved, but voltage gain may be reduced
Solution Approach 1:
The inverter circuit achieves both high switching speed and adequate voltage gain through its simplified single-stage architecture. The direct coupling between stages and the use of feedback eliminate the need for complex multi-stage amplifiers, enabling fast switching while maintaining sufficient gain through the regenerative feedback mechanism.
Solution Approach 2:
The feedback loop enhances voltage gain in the simplified circuit by using the output signal to reinforce the differential input. This allows the single-stage inverter to achieve the necessary gain without requiring multiple amplification stages, thereby maintaining high switching speed.
Data Source
AI summary
The LVDS receiver circuit comprises a differential-input transistor pair, a control transistor pair, a current-mirror-load circuit, a first feedback inverter and a second feedback inverter. The first feedback inverter, the second feedback inverter and the control transistor pair constitute a feedback loop. The voltage change of the input voltage of the first feedback inverter is suppressed, and the input voltage is controlled around the threshold voltage of the first feedback inverter.