Using NCAP to Predict RFI Effects in Linear Bipolar Integrated Circuits

Applications of the Nonlinear Circuit Analysis Program (NCAP) to calculate RFI effects in electronic circuits containing discrete semiconductor devices have been reported upon previously. The objective of this paper is to demonstrate that the computer program NCAP also can be used to calculate RFI effects in linear bipolar integrated circuits (IC's). The IC's reported upon are the μA741 operational amplifier (op amp) which is one of the most widely used IC's, and a differential pair which is a basic building block in many linear IC's. The μA741 op amp was used as the active component ent in a unity-gain buffer amplifier. The differential pair was used in a broad-band cascode amplifier circuit. The computer program NCAP was used to predict how amplitude-modulated RF signals are demodulated in the IC's to cause undesired low-frequency responses. The predicted and measured results for radio frequencies in the 0.050-60-MHz range are in good agreement. Contained in the paper is a complete set of NCAP parameter values for all the transistors in the μA741 op amp. These parameter values may be used as typical data for similar transistors in other bipolar integrated circuits.