RF Amplifier Ground Equalization for Accurate IDD Calibration
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Solution Overview
Problem
During automated test equipment (ATE) testing of RF integrated circuits, the increased resistance of test probes leads to inaccurate IDD calibration, resulting in reduced IC yield due to differences in ground voltages between the bias network and active circuit, causing higher current values when assembled into modules, which fail to meet specifications.
Innovation Solution
Incorporating an on-chip calibration switch or active feedback loop calibration circuit to equalize voltages between the bias network and active circuit during ATE testing, allowing for accurate IDD calibration without affecting noise performance during normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If automated test equipment with test probes is used to measure IDD current during calibration, then testing capability is enabled, but the increased resistance of test probes causes inaccurate calibration results
Solution Approach 1:
A calibration switch is introduced as an intermediary component connected between the bias network ground and the active circuit ground. During calibration, the switch closes to create a common ground reference, eliminating the measurement error caused by probe resistance. This intermediary structure allows accurate calibration despite the presence of high-impedance test probes.
Solution Approach 2:
The calibration switch is activated before the actual IDD measurement and calibration process. By closing the switch to equalize ground voltages prior to measurement, the system prepares the circuit in a known state that compensates for the inherent probe resistance, ensuring accurate calibration results from the outset.
2Productivity
If test probe resistance is present during calibration, then testing can proceed, but ground voltage differences cause incorrect current calibration
Solution Approach 1:
The calibration switch creates a feedback path that allows the bias network and active circuit to reference a common ground potential during calibration. This feedback mechanism continuously equalizes ground voltages, ensuring that the IDD calibration reflects the actual operating conditions without the error introduced by probe resistance.
3Device complexity
If calibration is performed without ground equalization, then testing is simpler, but modules fail to meet specifications after assembly
Solution Approach 1:
The calibration function is segmented from normal operation. The calibration switch is only activated during the calibration phase and remains open during normal circuit operation. This segmentation allows the additional ground equalization circuitry to be included without permanently increasing the complexity of the operational circuit, while ensuring specification compliance through accurate calibration.
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.