Communication interface having synthesized matching impedances for different frequency bands and a design method therefor

摘要

A communication interface and a design method therefor provide a synthesized terminating impedance matching different frequency bands on a communication circuit. In some cases, for example based on specified network requirements in a particular country, the terminating impedance presented by the interface must have different frequency characteristics for received signals in different bands of frequencies. A transconductance amplifier and feedback loop provide the terminating impedance for signals received from the communication circuit and serves as a source impedance for signals transmitted by the interface to the telephone line. Signals with different frequencies will generally be received from the telephone line. These different characteristics are realized using different filter networks in the feedback loop. Each network provides a matching terminating impedance to the communication circuit according to the frequency band applied to the circuit. The network shapes the synthesized impedance based upon the relation Z=1/GmH where Z=the terminating impedance; Gm is the transconductance of the amplifier and H is the transfer function of the feedback network. For multiple frequencies on the telephone line, multiple networks are included in the feedback loop. Each network is designed to match the impedance requirements of a frequency band without affecting the terminating impedance and frequency band of the other frequency bands.