PWM Receiver Bias Calibration for DC Offset Cancellation
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Solution Overview
Problem
Receiver circuits in communication devices face challenges with manual calibration processes, which are time-consuming and costly, and require additional calibration due to component aging and temperature variations, leading to errors in demodulation or decoding caused by voltage offset.
Innovation Solution
A receiver circuit with a self-calibration capability, featuring a resistor string, transistors, and switches, which automatically adjusts the DC operating point by measuring voltage differences and selectively closing switches to minimize offset, allowing for on-demand calibration without human intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual calibration processes are performed at manufacturing facility, then offset can be removed or reduced, but the process is time consuming and costly
Solution Approach 1:
The receiver circuit performs calibration automatically using its own internal resources (resistor strings, transistors, switches, and amplifier) without requiring external manual intervention. The circuit measures its own offset voltage and adjusts the bias accordingly, enabling self-calibration that eliminates time-consuming manual processes while maintaining offset removal accuracy
Solution Approach 2:
The calibration process is performed automatically during the startup sequence or before signal processing begins, preparing the circuit in advance for optimal operation. This preliminary automatic calibration ensures the circuit is ready for immediate use without requiring manual intervention during operation
2Measurement precision
If manual calibration is performed, then initial offset can be corrected, but additional calibration is required due to component aging and temperature variation
Solution Approach 1:
The receiver circuit continuously monitors its own offset voltage through the amplifier and automatically adjusts the bias using the resistor strings and switches when offset exceeds a threshold. This self-calibration capability handles both initial calibration and ongoing drift compensation due to aging and temperature variations, eliminating the need for repeated manual calibration interventions
Solution Approach 2:
The amplifier continuously provides feedback about the offset voltage condition to the calibration circuitry. When the offset exceeds a predetermined threshold, the feedback triggers automatic adjustment of the bias voltage through the resistor strings and switches, creating a closed-loop system that maintains accuracy despite component aging and temperature changes
3Power
If high gain amplifier is used, then signal amplification is improved, but small offset at input results in large voltage shift at output causing demodulation error
Solution Approach 1:
The calibration circuitry adjusts the bias voltage to compensate for offset before the amplifier processes the signal. By performing this offset cancellation in advance, the high-gain amplifier can operate at full gain without amplifying offset errors, thereby maintaining both signal amplification and demodulation accuracy
Solution Approach 2:
The resistor strings and switches act as an intermediary mechanism between the offset voltage and the amplifier input. By adjusting the bias voltage through this intermediary circuitry, the offset is canceled at the amplifier input, allowing the high-gain amplifier to amplify only the desired signal without introducing large offset-induced voltage shifts
Data Source
AI summary
A method for calibrating the DC operating point of a PWM receiver circuit is disclosed. The PWM receiving circuit includes an envelop detector having a first resistor string, and includes a bias circuit having a second resistor string and a plurality of switches. The second resistor string is coupled between a supply voltage and a reference voltage and functions as a voltage divider. Each switch, when closed, accesses a second voltage at a node of the second resistor string connected to the closed switch. To perform the calibration process, the plurality of switches is closed one at a time, and the second voltage is compared with a first voltage at a first node of the first resistor string. The switch that, when closed, produces the smallest difference between the first voltage and the second voltage remains closed after the calibration process, and is used for demodulating the PWM signal.