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Switched Transversal Filter

IP.com Disclosure Number: IPCOM000082650D
Original Publication Date: 1975-Jan-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Monrolin, J: AUTHOR

Abstract

In a transmission system, there is a need at the receiver end to retrieve the clock frequency from the received signal envelope. For this purpose, the difference of received signal amplitudes taken at instants distant from a signaling period T, is detected by filtering circuit represented in Fig. 1A. This circuit performs on the received signal applied to input I, a transfer function (1-e/-p/) in the given frequency band, tau being variable as a function of the baud rate.

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Switched Transversal Filter

In a transmission system, there is a need at the receiver end to retrieve the clock frequency from the received signal envelope. For this purpose, the difference of received signal amplitudes taken at instants distant from a signaling period T, is detected by filtering circuit represented in Fig. 1A. This circuit performs on the received signal applied to input I, a transfer function (1-e/-p/) in the given frequency band, tau being variable as a function of the baud rate.

The filter essentially comprises an operational amplifier A, a first plurality of N Transistor switches T1 to TN associated to capacitors C1 to CN, and an additional transistor switch TO associated to a capacitor CO. All transistors are normally OFF and are rendered conductive through pulses represented in Fig. 1B.

The frequency of pulses controlling the conduction of transistors T1 to TN is equal to the signaling frequency 1/T and the duration is T/N. Conduction of TO is controlled through pulses SO having a frequency 1/NT. N is chosen greater than three and in the illustrated circuit is equal to six.

Each capacitor C1 to C6 and transistor T1 to T6 operate in the same way at different instants controlled by pulses S1 to S6, to continuously generate on output 0 the desired voltage difference.

For example capacitor C3, when transistor T3 is ON, changes through the instantaneous input current i flowing in r.

The difference of changes Q on capacitor C3 at instants distan...