| 摘要 |
A microprocessor-controlled voltage source selectively provides to a telephone line either a DC or an AC voltage, prescribed characteristics of which are programmably adjustable, enabling test equipment to controllably condition and test the line with essentially any desired line conditioning voltage or signal waveform. A digital-to-analog converter (DAC) provides an output voltage having an amplitude that is digitally programmable. This output voltage is available to be applied either directly or through controlled amplifier circuitry to the line. In order to generate an AC signal having both an adjustable amplitude and waveform characteristic, the output of the DAC sets the amplitude for a combination of signals from a plurality of squarewave generators having programmable frequency characteristics. The output of the combining unit is coupled to a switched capacitor filter which filters the controllably-interrupted, digitally-controllable output voltage, (e.g., removes odd harmonics from the fundamental frequency of the desired waveform) and an adjustable smoothing filter, which is coupled to the switched capacitor filter and removes the 'stairstep' transitions in the waveform associated with the operation of the switched capacitor filter. The output of the smoothing filter is coupled to an output amplifier which amplifies the AC waveform output of the adjustable smoothing filter.
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