RF Amplifier IDD Calibration with Ground Equalization
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Solution Overview
Problem
During automated test equipment (ATE) testing of RF integrated circuits, particularly those with cascode-based active circuits, the variation in test probe resistance leads to inaccurate IDD calibration, resulting in reduced IC yields due to differences in ground voltages between the bias network and the active circuit, causing higher current values when assembled in modules.
Innovation Solution
Incorporating an on-chip calibration switch or feedback loop calibration circuit to equalize the ground voltages between the bias network and the active circuit during calibration, ensuring accurate IDD setting and preventing noise injection at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If automated test equipment is used to calibrate IDD during manufacturing, then productivity is improved, but measurement precision deteriorates due to test probe resistance variation
Solution Approach 1:
A calibration switch is introduced as an intermediary component between the test probe and the bias network ground connection. During calibration, the switch connects the test probe ground to the bias network ground, providing a low-impedance path that eliminates the effect of test probe resistance variation. This allows accurate IDD calibration while maintaining high manufacturing throughput.
2Measurement precision
If ground voltages are equalized during calibration, then measurement precision is improved, but device complexity increases due to additional calibration circuitry
Solution Approach 1:
The calibration function is extracted as a separate, dedicated circuit block with a calibration switch and calibration resistor. This modular approach allows the calibration functionality to be added without significantly increasing the complexity of the main amplifier circuit. The calibration components are isolated and can be independently controlled.
Solution Approach 2:
The calibration ground equalization is performed as a preliminary action before the amplifier is put into normal operation. The calibration switch is activated only during the calibration phase to equalize ground voltages, and then deactivated for normal operation. This timing separation allows the calibration function to be implemented without permanently increasing circuit complexity.
3Manufacturing precision
If calibration switch is used to equalize ground voltages, then manufacturing precision is improved, but loss of energy increases due to additional current paths
Solution Approach 1:
The calibration resistor is designed with a resistance value that is sufficiently low to provide an accurate calibration path, but not so low as to cause excessive current draw. The calibration switch is activated only for the brief duration needed to perform IDD calibration, minimizing the total energy consumed during the calibration process.
Data Source
AI summary
Circuits and methods for improving IC yield during automated test equipment (ATE) calibration of circuit designs which require IDD calibration and use a closed feedback bias circuit, such as amplifier circuits. The circuit designs include bias branch/active circuit architectures where the active circuit includes one or more active devices. An example first embodiment uses an on-chip calibration switch between the on-chip grounds of a bias network and an active circuit comprising an amplifier. During calibration of the active circuit by the ATE, the calibration switch is closed, and after completion of calibration, the calibration switch is opened. An example second embodiment utilizes an active on-chip feedback loop calibration circuit to equalize voltages between the on-chip grounds of a bias network and an active circuit comprising an amplifier during calibration of the active circuit. Both embodiments mitigate or overcome miscalibration of active circuit current settings resulting from ATE test probe resistance.