TELEPHONY TEST SYSTEM WITH ADJUSTABLE OUTPUT IMPEDANCE

摘要

A telephony test system (2) includes a controller (4), a programmable gate array (PGA) (24) and a digital signal processor (DSP) (26) connected by a common bus (20). The PGA (24) includes an outpout connected to an input of a digital-to-analog converter (DAC) (36) and input connected to an output of an analog-to-ditigal converter (ADC) (32). A driver circuit (46) is connected between the DAC (36) and a telephone circuit (60) and between the ADC (32) and the telephone circuit (60). Under the control of the DSP (26), the driver circuit (46) generates voltages to the telephone circuit (60) and samples the response of the telephone circuit (60) to such generated voltages. The driver circuit (46) includes control inputs for receiving from the PGA (24) an impedance adjust signal (D) and a resistance adjust signal (R). An output impedance (124) of the driver circuit (46) connected to the telephone circuit (60) is adjustable as a function of the impedance adjust signal (D) and/or the resistance adjust signal (R).