Browse Prior Art Database

Encoder

IP.com Disclosure Number: IPCOM000092777D
Original Publication Date: 1967-Jan-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Aldrich, DH: AUTHOR [+3]

Abstract

The unknown analog signal x is applied simultaneously to 2/n/-1 voltage comparator circuits 10. The final number of bits to be encoded is n. Each comparator 10 is referenced by connector lead 15 to a different fraction of the full-scale voltage E by precision resistor network 11. The latter includes a plurality of equal resistors 12 connected in series. Network 11 establishes the 2/n/ increments contained in the voltage range 0 to E. The first comparator 10 is referenced to 2/-n/E, the second 2(2/-n/E), the third 3(2/-n/E), etc. If x, where 0 Less than - Equal to x Less than - Equal to E, is less than a comparator reference, the comparator 10 has a binary 0 output. If the unknown signal x is greater than the comparator reference, the comparator 10 has a binary 1 output.

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Encoder

The unknown analog signal x is applied simultaneously to 2/n/-1 voltage comparator circuits 10. The final number of bits to be encoded is n. Each comparator 10 is referenced by connector lead 15 to a different fraction of the full-scale voltage E by precision resistor network 11. The latter includes a plurality of equal resistors 12 connected in series. Network 11 establishes the 2/n/ increments contained in the voltage range 0 to E. The first comparator 10 is referenced to 2/-n/E, the second 2(2/-n/E), the third 3(2/-n/E), etc. If x, where 0 Less than - Equal to x Less than - Equal to E, is less than a comparator reference, the comparator 10 has a binary 0 output. If the unknown signal x is greater than the comparator reference, the comparator 10 has a binary 1 output. Thus all comparators 10 referenced to voltages below the unknown read 1's. All comparators referenced above the unknown read 0's. With this information it is possible to decode the comparator outputs into n different lines. This results in a parallel binary word of n bits proportional to the magnitude of x.

The output segments of comparators 10 are connected to level translators
13. Such is for the purpose of translating and modifying comparator outputs so that they are compatible with the logic circuits.

A preferred comparator 10 comprises a differential amplifier of the current mode switch type. A DC current flows in emitter resistor RE, which can be directed either to the collector circuit of Q1 or to the collector circuit of Q2. This depends upon the relative polarity of x with respect to Eref, where Eref is the divided-down fraction of E for a particular stage. The transition region, which occurs near the point where x = Eref, is approximately 100 mv wide. This dictates that conversions of signals which differ from the reference by less than 100 mv cannot reliably be done. Transistor Q3 is an emitter-follower which serves the dual purpose of providing a good output drive capability and a le...