US 8,508,304 B2Granted

Serdes VCO with phased outputs driving frequency to voltage converter

AssigneeTexas Instruments Incorporated

InventorVishnu Ravinuthula

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Abstract

Reducing a gain of a VCO, which may be used in a serdes system, includes using an oscillator replicating the VCO. The oscillator frequency varies according to PVT conditions of circuit elements of the oscillator, which affect a speed of the circuit elements. A first circuit receives an output of the oscillator to produce a current that varies inversely proportionally to the oscillator frequency. A second circuit injects the current into a power supply line of the VCO. Thus, high VCO frequencies can be attained. By reducing the gain of the VCO, thermal noise contribution of the loop resistor and the loop capacitor required for desired loop bandwidth are reduced. During fast corner conditions, minimal current is injected into the VCO. During slow corner conditions, high current is injected into the VCO. These help keep VCTRL of the PLL loop close to a mid-rail operating region.

Claims3

Dependent claims

A serdes system, comprising:

A. a voltage controlled oscillator including a ring oscillator having a power supply line and a reference supply line for providing clock pulses to at least a part of the serdes system;
B. a replica oscillator coupled between the power supply line and the reference supply line and having four, phased output lines;
C. a frequency to voltage converter coupled between the power supply line and the reference supply line and having four inverters, each inverter having an input coupled to one of the four, phased output lines of the replica oscillator, the inverters having outputs coupled together on one output line;
and
D. an operational amplifier having first and second stages that are coupled between the power supply line and the reference supply line and that are coupled together, the first stage having an input coupled to a reference voltage line, and the second stage having an input coupled to the one output line of the frequency to voltage converter and an output coupled to the power supply line of the voltage controlled oscillator.

2 more elements

Dependencies are inferred from the claim text.

Facts

Application: 13/274,602Filed 17 Oct 2011
Published: US 2013/0093526 A118 Apr 2013
Granted: 13 Aug 2013
Term ends: Not estimatedThe source records don’t support an estimate.

Classification5 codes

H03L 7/0995
Concerning mainly the controlled oscillator of the loop: the oscillator comprising a ring oscillator
H03K 3/013
Details: modifications of generator to prevent operation by noise or interference
H03K 3/0315
Astable circuits: ring oscillators
H03L
Automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or