# US 7,609,799 B2 · Circuit, system, and method for multiplexing signals with reduced jitter

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- Number: US 7,609,799 B2
- Document ID: US7609799B2
- Status: Granted
- Kind: B2
- Application number: 11/468,195
- Filed: 2006-08-29
- Published: 2007-03-08
- Granted: 2009-10-27
- Earliest claimed: 2005-09-02
- Assignees: Cypress Semiconductor Corporation
- Inventors: Gabriel Li
- Web page: https://patentgrep.com/patent/US7609799B2

## CPC

- H04J 3/047: {Distributors with transistors or integrated circuits}
- H03K 19/1737: {using multiplexers (H03K19/1738 takes precedence)}
- H03K 17/002: {Switching arrangements with several input- or output terminals (code converters H03M5/00, H03M7/00)}
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)
- 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 multiplexer circuit, system and method is provided herein for multiplexing signals with reduced jitter by eliminating all crosstalk and power supply noise injection within the multiplexer circuit. For example, crosstalk and supply noise injection may be eliminated by: (i) separating the multiplexing function into three separate logic gates and (ii) allowing only one switching input per logic gate. In some cases, jitter may be further reduced by distributing the logic gates across three distinct power domains. In other words, the logic gate inputs may be further isolated by gating each signal in its own power domain. In addition, the multiplexer circuit provides built in delay matching by utilizing three substantially identical logic gates.

## Claims

### Claim 1

A circuit comprising:
a first logic gate arranged within a first power supply domain and coupled for receiving a first signal;
a second logic gate arranged within a second power supply domain and coupled for receiving a second signal;
a logic block arranged within a third power supply domain and coupled for supplying a control signal to the first and second logic gates for deactivating one of the first and second signals; and
a third logic gate arranged within a fourth power supply domain and coupled to outputs of the first and second logic gates for transmitting either the first signal or the second signal, whichever has not been deactivated by the logic block.

### Claim 2 (depends on 1)

The circuit of claim 1, wherein the first, second and third logic gates each comprise a two-input NAND gate.

### Claim 3 (depends on 1)

The circuit of claim 1, wherein the first, second and third logic gates each comprise a two-input NOR gate.

### Claim 4 (depends on 1)

The circuit of claim 1, wherein the control signal is coupled to a first input of the first logic gate and a first input of the second logic gate.

### Claim 5 (depends on 4)

The circuit of claim 4, wherein the first signal is coupled to a second input of the first logic gate, and the second signal is coupled to a second input of the second logic gate.

### Claim 6 (depends on 5)

The circuit of claim 5, wherein the first and second signals comprise clock signals.

### Claim 7 (depends on 5)

The circuit of claim 5, wherein the first and second signals comprise data signals.

### Claim 8 (depends on 5)

The circuit of claim 5, wherein outputs of the first and second logic gates are respectively coupled to a first and second input of the third logic gate in the third power supply domain.

### Claim 9 (depends on 8)

The circuit of claim 8, wherein an output of the third logic gate is coupled to a buffer circuit arranged within a fourth power supply domain of the circuit.

### Claim 10

A system, comprising:
a circuit comprising three logic gates and a logic block, each arranged within a separate power domain, wherein:
a first of the three logic gates is coupled for receiving a first signal;
a second of the three logic gates is coupled for receiving a second signal; and
a third of the three logic gates is coupled for receiving only one of the first and second signals, depending on a state of a control signal supplied to the first and second logic gates from the logic block; and
at least one system component coupled to an output of the third logic gate for receiving the only one of the first and second signals.

### Claim 11 (depends on 10)

The system of claim 10, wherein the first, second and third logic gates each comprise a NAND gate.

### Claim 12 (depends on 10)

The system of claim 10, wherein the first, second and third logic gates each comprise a NOR gate.

### Claim 13 (depends on 10)

The system of claim 10, wherein the first, second and third logic gates each comprise an identical logic gate.

### Claim 14 (depends on 10)

The system of claim 10, wherein the first and second signals comprise clock signals.

### Claim 15 (depends on 14)

The system of claim 14, further comprising one or more phase shift apparatuses coupled to the circuit for supplying the first and second signals thereto.

### Claim 16 (depends on 15)

The system of claim 15, wherein the one or more phase shift apparatuses each comprise a device selected from a group comprising a phase locked loop (PLL) device and a delay locked loop (DLL) device.

### Claim 17

A method for multiplexing signals with reduced jitter, the method comprising:
supplying a first signal to a first logic gate and a second signal to a second logic gate;
deactivating one of the first or second signals by supplying a control signal to the first and second logic gates; and
forwarding an active one of the first or second signals to a third logic gate, wherein the steps of deactivating and forwarding enable the first and second signals to be multiplexed with reduced jitter, and wherein the first, second and third logic gates are spaced apart from one another and respectively arranged within a first, second and third power domain.

### Claim 18 (depends on 17)

The method of claim 17, wherein the first and second signals comprise clock signals.

### Claim 19 (depends on 17)

The method of claim 17, wherein the fist and second signals comprise data signals.