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Anti-Saturating ANR Cable Receiver

IP.com Disclosure Number: IPCOM000041269D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Gorga, KJ: AUTHOR [+2]

Abstract

A typical ANR (IBM 3277-2 Terminal Interface) cable receiver consists of a voltage comparator whose threshold voltage is set at a midpoint value of the expected ANR signal swing. However, care must be taken in the design of this receiver to prevent saturation on long cable runs when noise and ringing are a problem. Fig. 1 shows a typical ANR signal waveform. In the receiver design (Fig. 2), R1 is a cable-terminating resistor. A high speed voltage comparator is used to translate the ANR signal levels to TTL logic levels. The input voltage, on the comparator operated in this configuration must be maintained between approximately 1.6-4.8 volts. Diodes D1 and D2 prevent the input from falling below 1.4 volts plus the VCE(sat) of the driver transistor.

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Anti-Saturating ANR Cable Receiver

A typical ANR (IBM 3277-2 Terminal Interface) cable receiver consists of a voltage comparator whose threshold voltage is set at a midpoint value of the expected ANR signal swing. However, care must be taken in the design of this receiver to prevent saturation on long cable runs when noise and ringing are a problem. Fig. 1 shows a typical ANR signal waveform. In the receiver design (Fig. 2), R1 is a cable-terminating resistor. A high speed voltage comparator is used to translate the ANR signal levels to TTL logic levels. The input voltage, on the comparator operated in this configuration must be maintained between approximately 1.6-4.8 volts. Diodes D1 and D2 prevent the input from falling below 1.4 volts plus the VCE(sat) of the driver transistor. Resistors R2 and R4, along with the voltage drop across diodes D1 and D2, limit the highest ANR cable voltage at the input of the comparator to 5.0 volts. Diodes D3 and D4 clamp the ANR cable voltage to approximately ground and supply for transients. R3 and R5 set the comparator threshold voltage. This circuit has proven not to saturate on ANR cable lines that are in excess of specification cable length.

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