US 5,426,384 AGranted

Voltage controlled oscillator (VCO) with symmetrical output and logic gate for use in same

AssigneeMotorola, Inc.

InventorMichael R. May

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Abstract

A voltage controlled oscillator (VCO) (23) includes a periodic signal generator (30) such as a comparator (42)followed by a latch (43), and a logic gate such as a NAND gate (31) connected to the output of the latch (43) to adjust for asymmetries in the output signals from the latch (43). In one embodiment, the NAND gate (31) includes two pullup transistors (80, 81) receiving first and second output signals from the latch and connected between a first power supply voltage terminal and an output node (86). Two switching branches (82, 83 and 84, 85) each including two transistors are connected between the output node (86) and a second power supply voltage terminal. The order of the input signals received by the two transistors is reversed between the two switching branches (82, 83 and 84, 85) to compensate for any duty cycle asymmetries. A frequency divider (32) divides the output of the NAND gate (31) to complete the duty cycle adjustment.

Claims12

Dependent claims

A voltage controlled oscillator (VCO) with a symmetrical output comprising:

a periodic signal generator having an input terminal for receiving an input voltage, and first and second output terminals for respectively providing a first signal and a second signal of a periodic differential output signal;
and
a logic gate having first and second input terminals respectively coupled to said first and second output terminals of said periodic signal generator, and an output terminal coupled to an output node, comprising:
a first switching element having a first terminal coupled to a first power supply voltage terminal, a second terminal coupled to an output node providing an output signal of the VCO thereon, and a control terminal for receiving said first signal;
a second switching element having a first terminal coupled to said first power supply voltage terminal, a second terminal coupled to said output node, and a control terminal for receiving said second signal;
a third switching element having a first terminal coupled to said output node, a second terminal coupled to a second power supply voltage terminal, and first and second control terminals respectively receiving said first and second signals, said third switching element including first and second switching subelements serially coupled between said output node and said second power supply voltage terminal respectively responsive to said first and second signals;
and
a fourth switching element having a first terminal coupled to said output node, a second terminal coupled to said second power supply voltage terminal, and first and second control terminals respectively receiving said second and first signals, said fourth switching element including third and fourth switching subelements serially coupled between said output node and said second power supply voltage terminal respectively responsive to said second and first signals.

5 more elements

A differential input to single-ended output comparator with a symmetrical output, comprising:

an input comparator having positive and negative input terminals for respectively receiving first and second input signals of a periodic differential input signal, and positive and negative output terminals;
a differential latch having first and second input terminals respectively coupled to said positive and negative output terminals of said comparator, and first and second output terminals for respectively providing first and second signals;
and
logic gate having a first input terminal coupled to said first output terminal of said differential latch, a second input terminal coupled to said second output terminal of said differential latch, and an output terminal for providing an output signal of the comparator;
whereby said output signal of the comparator is symmetrical.

2 more elements

Dependencies are inferred from the claim text.