Circuit for monitoring BJT RF performance using DC measurements

A test circuit is described for on-wafer monitoring of high-frequency performance of bipolar junction transistors 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 transistors' 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/.