The Hybrid Integration of a Multistage Active Bandpass Filter/Amplifier

This paper describes the fabrication, characterization, and analysis of a hybrid microcircuit to be used as a signal amplifier and conditioner for an IR tracking system. The entire circuit is integrated on a 1 X 2-in alumina substrate using thick-film resistors and conductors, some chip resistors in critical locations, chip capacitors, and monolithic integrated-circuit (IC) operational-amplifier (op-amp) chips. Fig. 1 shows a block diagram of the entire circuit. The transfer functions of each of the stages is derived. The predicted gain. peak and the shape of the measured bandpass agree well with experimental results. The computer simulation using an opamp "macromodel" [1] gives results very closely resembling the measured bandpass, and underscores the utility of computer circuit simulations in IC development. Stability and hybrid layout considerations are discussed. The noise figure is measured as a function of frequency for the given system source impedance of 5 M and also for 0.5 M to indicate the dependence of the noise figure on source resistance. The dominant sources of noise in the amplitier/filter and low-noise design considerations are discussed.