| 摘要 |
A symmetric finite impulse response filter for receiving a digital input signal and generates a filtered analog output signal for application to a balanced line, such as a tip and ring lead pair. Logic levels of predetermined symmetrical bit pairs of the digital input signal are detected and in response, predetermined corresponding capacitors are selectively switched between bias and reference voltages, thereby charging predetermined voltages proportional to the capacitances of the capacitors. The predetermined voltages are summed in an operational amplifier which, in response produces a filtered analog output signal. Individual capacitors are utilized for realizing each pair of symmetrical coefficients of the filter transfer function, resulting in considerable economy of size. A switched capacitor implementation results in high speed performance, simple design and low cost.
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