| 摘要 |
<p>An operational amplifier (18) capable of selectively performing a variety of circuit functions. A single operational amplifier (18) utilizes switched capacitors (24, 32 and 36) for sampling and holding an input signal VIN, for establishing a low frequency pole, for applying the sample to an output capacitance (47 and 48) to charge the capacitance (47 and 48) and for comparing the input signal VIN with a reference VAG. The multi-function circuit (12) provides a large savings in circuit area and permits versatility of circuit applications. One embodiment of the invention is to utilize a companding DAC (14) having a capacitor array which may be used as the output capacitance (47 and 48) of the operational amplifier circuit (12). The DAC (14) provided utilizes an R ladder DAC (52) coupled directly to a C DAC (50) and has a switching structure that is simpler than comparable prior art circuits. The DAC (14) is asynchronous and has programmable A- and Mu-255 law PCM conversion capability. Coupled directly to the C DAC (50) is an operational amplifier receive filter circuit (16) which utilizes the C DAC (50) as an input capacitor thereby eliminating the need for a buffer amplifier and allowing the DAC (14) to be used for both analog to digital and digital to analog conversion.</p> |
