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A LOW POWER, LOW VOLTAGE, FREQUENCY LOCKED CURRENT MODE OSCILLATOR

IP.com Disclosure Number: IPCOM000008038D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-14
Document File: 3 page(s) / 133K

Publishing Venue

Motorola

Related People

James Phillips: AUTHOR

Abstract

As competitive pressure on the IC industry pushes supply voltages to 1.8 volts and battery life in portable wireless products becomes a priority, circuits employing CMOS analog integrated signal processing techniques must be developed to meet these goals.

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MOTOROLA Technical Developments

A LOW POWER, LOW VOLTAGE, FREQUENCY LOCKED CURRENT MODE OSCILLATOR

by James Phillips

  As competitive pressure on the IC industry pushes supply voltages to 1.8 volts and battery life in portable wireless products becomes a priority, circuits employing CMOS analog integrated signal processing techniques must be developed to meet these goals.

  One way to meet these challenges is to operate circuits in the current, rather than the voltage domain for the two following reasons:

  1) Due to the square nature of the I-V relation- ship of a MOSFET's drain current as a function of gate voltage, very large current signal swings can be processed with very little voltage swing. This allows large current signals to be processed at a very low supply voltage.

  2) The bandwidth of the basic current amplifier building block can actually be used as part of the overall desired response rather than designing volt-

age amplifiers that need bandwidths an order of magnitude greater than the desired response, thus saving overall current drain because bandwidth is proportional to current drain.

  Existing current amplifier technology can exhibit the properties of operating at 1.8 supply voltage and having a single pole lowpass response that can be "tuned" by modulating a bias current in a feedback loop. This allows equivalent RC time constants to be tuned to within 1.0 percent imple- mented with current amplifiers, whereas real RC time constants can vary by as much as 50 percent over process and temperature variation.

  The block diagram below shows a possible way of tuning all the on-chip current amplifiers such that their properties remain constant over process and temperature variation and allow the IC designer to implement various signal processing architectures with a high degree of precision:

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FREQUENCY CONTROL LOOP 1

CURRENT FEEDBACK

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FREQUENCY

Fig. 1

0 Momm,a, Inc. ,997 96 March 1997

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0 M M-OLA

Technical Developments

  The oscillator block consists of two single pole lowpass differential current amplifiers and three current attenuators, respectively marked CA and ATTN.

  In order to keep the amplitude of oscillations from growing without bound or damping out, a feedback bias current is maintained such that the amplitude of the os...