Circuit for monitoring BJT RF performance using DC measurements
Robert M. Fox, R. Chawla, William R. Eisenstadt, D. Hemmenway, J. Johnston · 2002
A test circuit is described for on-wafer monitoring of high-frequency performance of bipolar junction transistors (BJTs) using only DC measurements. The test circuit includes an oscillation-amplitude detector and a high-frequency (/spl sim/3 GHz) oscillator whose minimum bias current for oscillation (I/sub osc/) correlates strongly with the transistor maximum oscillation frequency (f/sub max/). Variations in the circuit's I/sub osc/ can be routinely monitored to track changes in f/sub max/ caused by process variations. Monte Carlo simulations showed a correlation coefficient of -0.79 between I/sub osc/ and f/sub max/. Variations in measured f/sub max/ intentionally introduced through layout variations were verified to be strongly correlated with I/sub osc/.