Nec Corporation

Takashi Shinozuka

Toshio Suzuki

Masanobu Arai

Takao Hayashi

Satoshi Hiraide

In addition to an information signal subjected to a frequency dependent and a frequency independent loss component and delivered to an automatic equalizer through a transmission path which is typically a subscriber's communication path between a subscriber's terminal equipment and an exchange, an equalizer input signal comprises a pilot signal subjected to the frequency independent loss component alone. The equalizer comprises a first equalizer (26, 27, 36) responsive to a pilot signal component derived from the pilot signal for compensating for the frequency independent loss component. A second equalizer (31, 32, 37) compensates for the frequency dependent loss component in response to an information signal component derived from the information signal. The first and the second equalizers are cooperative in various manners in equalizing the input signal into an equalizer output signal. The pilot and the information signal components are extracted either directly or indirectly from the input signal. The output signal is fed back to a frequency dependent component detector (31) either directly or indirectly.

Equalizer for frequency independent and dependent transmission loss

In a subscriber line interface circuit of a telephone switching system, a differential amplifier (1) is coupled through the line terminals (T, R) of a two-wire subscriber line for detecting a voltage difference developed thereacross. First and second resistances (8, 9) of equal values are coupled at their first ends to the line terminals, respectively. Tip and ring drivers (2, 3) are connected to the other end of first and second resistances for driving the load impedance of the subscriber line. First, second and third feedback loops (f.sub.1, f.sub.2, f.sub.3) are provided, the first feedback loop being coupled from an output of differential amplifier (1) to the input of the drivers (2, 3) vary the impedance characteristics of the first and second resistances (8, 9) so that a high impedance is synthesized across each of the first and second resistances. The second and third feedback loops are also coupled from the output of differential amplifier (1) to the drivers (2, 3), each of the second and third feedback loops having a different passband frequency characteristic and having the effect of reducing the synthesized impedances to a predetermined value.

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Tokyo, Japan

Takashi Shinozuka