# US 4,392,067 A · Logic select circuit

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- Number: US 4,392,067 A
- Document ID: US4392067A
- Status: Granted
- Kind: A
- Application number: 06/235,397
- Filed: 1981-02-18
- Granted: 1983-07-05
- Earliest claimed: 1981-02-18
- Assignees: Motorola, Inc.
- Inventors: John J. Price, Jr.
- Web page: https://patentgrep.com/patent/US4392067A

## CPC

- H03K 19/017509: {Interface arrangements}
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)

## Abstract

A circuit for use with interface systems for providing a threshold setting function wherein the system can be made to interface with T.sup.2 L or CMOS logic with either 5 or 15 volt power supply capabilities. The circuit comprises a pair of matched resistors coupled in series to one another. The first one of the resistors is returned to a select terminal via a first pair of diodes. The second resistor is returned to a terminal at which may be supplied a ground reference potential via a second pair of diodes. A source of current is provided that is coupled to the interconnection of the second resistor with the second pair of diodes. A threshold output is provided to the interface system at the interconnection between the serially connected resistors.

## Claims

### Claim 1

A logic select circuit for providing a multi-level logic threshold signal at an output thereof, comprising:
first diode means coupled between a first terminal and a first circuit node;
second diode means coupled between a second terminal at which is supplied a ground reference potential and a second circuit node;
circuit means coupled between said first and second circuit nodes and to the output of the logic select circuit; and
current source means coupled to said second circuit node for providing a predetermined current thereto such that a first logic threshold signal of a first level is produced at the output of the logic select circuit and second logic threshold signal of a second level is produced when said first terminal is connected to a source of operating potential supplied to the logic select circuit.

### Claim 2 (depends on 1)

The logic select circuit of claim 1 wherein:
said first diode means includes first and second serially connected diodes; and
said second diode means includes third and fourth serially connected diodes.

### Claim 3 (depends on 2)

The logic select circuit of claim 2 wherein said circuit means includes:
a first resistor; and
a second resistor connected in series with said first resistor with the output of the logic select circuit being coupled to the interconnection point between said first and second resistors.

### Claim 4

A monolithic integrated logic select circuit for providing multiple logic threshold signals to an utilization means, comprising:
first and second circuit means serially connected between a first terminal and a second terminal, said first and second circuit means having substantially identical voltage/current transfer characteristics wherein a first logic threshold signal of a first level is produced at the interconnection between said first and second circuit means when an operating potential is applied at said first terminal, said first logic threshold signal having a magnitude substantially equal to one-half said operating potential, said second terminal receiving a ground reference potential;
current source means for supplying a current of predetermined magnitude to said second circuit means wherein a second logic threshold signal of a second level is produced at the interconnection between said first and second circuit means whenever said first terminal is open-circuited;
output circuit means coupled to the interconnection between said first and second circuit means for supplying said first and second logic threshold signals to the utilization means; and
said first circuit means including a first diode, a second diode and a first resistor serially connected between said first terminal and a circuit node, said circuit node being coupled to said output circuit means.

### Claim 5 (depends on 4)

The logic select circuit of claim 4 wherein said second circuit means includes a third diode, a fourth diode, said third and fourth diode being serially coupled to said second terminal and a second resistor coupled between said serially coupled third and fourth diodes and said circuit node, said current source means being coupled to said third and fourth serially coupled diodes.