Voltage Shifter Coupling for Low-Reference ADC Interfaces
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Solution Overview
Problem
Radar device receiver circuits face challenges in interfacing with analog-to-digital converters (ADCs) having different supply voltages, as existing solutions like direct current blocking capacitors alter frequency response and are impractical for integrated circuits.
Innovation Solution
A system utilizing a variable gain amplifier and voltage followers, with a replica amplifier to match components and adjust voltage levels, enabling direct coupling between the radar device's baseband module and ADCs with different supply voltages, ensuring the signal is within the ADC's input voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a direct current blocking capacitor is inserted in the signal path to interface circuits with different power supplies, then the voltage level mismatch between amplifier and ADC is resolved, but the frequency response is altered and frequencies close to direct current are attenuated
Solution Approach 1:
The patent introduces an intermediary voltage shifting circuit between the amplifier and ADC. This circuit includes a resistor connected to the amplifier output and a voltage source that provides a DC offset voltage equal to the difference between the amplifier's common-mode voltage and the ADC's reference voltage. The voltage shifter transfers the amplifier signal to the ADC voltage domain without blocking DC components, thus resolving the voltage level mismatch while preserving the complete frequency response including DC and low-frequency signals.
2Loss of information
If large values of capacitance are used in the blocking capacitor to mitigate frequency response effects, then the attenuation of low frequencies is reduced, but the capacitor consumes significant area when implemented on an integrated circuit
Solution Approach 1:
The patent replaces the large-value blocking capacitor with an intermediary voltage shifting circuit consisting of a resistor and a voltage source. This intermediary approach achieves the same voltage level translation function without requiring large capacitance values, thereby eliminating the area consumption problem on integrated circuits while preserving the complete frequency response including DC components.
Solution Approach 2:
The patent changes the fundamental parameter approach from using capacitance (C) to control voltage translation to using resistance (R) combined with a voltage source (V_offset). This parameter change allows DC and low-frequency signals to pass through without attenuation, as the voltage shifter actively maintains the correct voltage level relationship without relying on capacitive coupling that blocks DC.
3Reliability
If the amplifier output voltage exceeds the ADC input voltage range or supply voltage, then the amplifier cannot communicate with the ADC, but inserting a blocking capacitor introduces high-pass filtering that changes system frequency response
Solution Approach 1:
The patent introduces a voltage shifting circuit as an intermediary between the amplifier and ADC. This circuit includes a resistor connected to the amplifier output and a voltage source that provides a DC offset equal to the voltage difference between the two circuits. The voltage shifter actively translates the amplifier's voltage domain to match the ADC's voltage domain, enabling reliable signal communication without introducing high-pass filtering or requiring large capacitors.
Solution Approach 2:
The patent changes the approach from passive capacitive voltage translation to active voltage shifting using a resistor and voltage source. This parameter change allows the system to handle DC and low-frequency signals reliably while maintaining a simpler signal path without large capacitors, thus reducing device complexity while improving communication reliability.
Data Source
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AI summary
A device includes a variable gain amplifier, a voltage shifter, a variable gain amplifier half replica module, and an analog to digital converter. The variable gain amplifier includes an input terminal to receive an input signal, an output terminal to provide a first output signal that is biased based on a first common-mode voltage reference. The voltage shifter circuit includes first and second input terminals, and an output terminal to provide, to the analog to digital converter, a third output signal that is biased based on a second common-mode voltage reference. The variable gain amplifier half replica module includes an output terminal coupled to the second input terminal of the voltage shifter circuit, the variable gain amplifier half replica module to control the third output signal of the voltage shifter circuit based on the first common-mode voltage reference and the second common-mode voltage reference.