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Low Power N-Way Analog Multiplexer

IP.com Disclosure Number: IPCOM000041311D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Pantani, JP: AUTHOR [+2]

Abstract

The following circuit will perform the multiplexing function of N analog data inputs (way 1,... way N) to an analog output under the control of n control bits (N = 2n). Only a few transistors are used in this multiplexer. Each of them has a specific function which may be analyzed as follows: Transistor 01 forms a common current source for both logic and analog portions of the circuit. Transistors 11...; 21...; 31, 32, 33, 34 form the differential pairs of stage n; ..., stage 2; stage 1, respectively. All differential pairs are standard current switch logic. Transistors 41, 42; 43, 44; 45, 46; ...; 47, 48 are respectively the input stages of way 1, way 2, way 3... way N. Transistor 02 is the current source for the output stage only.

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Low Power N-Way Analog Multiplexer

The following circuit will perform the multiplexing function of N analog data inputs (way 1,... way N) to an analog output under the control of n control bits (N = 2n). Only a few transistors are used in this multiplexer. Each of them has a specific function which may be analyzed as follows: Transistor 01 forms a common current source for both logic and analog portions of the circuit. Transistors 11...;
21...; 31, 32, 33, 34 form the

differential pairs of stage n; ..., stage 2; stage 1,

respectively. All differential pairs are standard current

switch logic. Transistors 41, 42; 43, 44; 45, 46; ...; 47, 48 are

respectively the input stages of way 1, way 2, way 3... way

N. Transistor 02 is the current source for the output stage

only. Transistors 51, 52 form an active load which is common

for all input stages. Transistor 53 forms an output stage which is common for the entire multiplexer circuit. Basic operation is as follows: When: BIT 1 = BIT 2 = ... = BIT n = GENERAL DISABLE =

UP LEVEL, current from transistor 01 flows through transistors 11, 21, 31, and biases input stage 41, 42 of way 1. The output voltage is then equal to the voltage of way 1, without interference of any other input stages. The

General Disable command isolates the output stage from ALL

input stages, by turning off transistors 01 and 02. The

output is high impedance within the following range: - positive power supply, minus one volt - negative power supply, pl...