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FIXED DUTY CYCLE PULSE GENERATING CIRCUIT WITH ADJUSTABLE FREQUENCY

IP.com Disclosure Number: IPCOM000005780D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2001-Nov-06
Document File: 2 page(s) / 84K

Publishing Venue

Motorola

Related People

David Overton: AUTHOR [+2]

Abstract

In some integrated circuit applications, a pulse generator is needed which provides an accurately controlled duty cycle and frequency. The circuit shown in Figure 1 utilizes an adjustable current reference, acurrent-controlled ring oscillator and a current-controlled pulse generator to provide a pulse train with a fixed and accurate duty cycle. The pulse frequency can be set to a desired value by adjusting the output of the current reference.

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MOTOROLA Technical Developments Volume 9 August 1989

FIXED DUTY CYCLE PULSE GENERATING CIRCUIT WITH ADJUSTABLE FREQUENCY

by David Overton and Gary Pace

   In some integrated circuit applications, a pulse generator is needed which provides an accurately controlled duty cycle and frequency. The circuit shown in Figure 1 utilizes an adjustable current reference, acurrent-controlled ring oscillator and a current-controlled pulse generator to provide a pulse train with a fixed and accurate duty cycle. The pulse frequency can be set to a desired value by adjusting the output of the current reference.

   The seven stage ring oscillator is composed of transistors Ql through Q6, l2L gate Q7, bias transistors Q12 and Q13, and pn junction capacitors Cl and C2. The period of the ring oscillator output signal is propor- tional to Kl/lbiasl where Ki is a proportionality constant which represents the product of pn junction capacitance and transistor base-emitter forward voltage drop. Bias current lbiasl is set by the current reference. The output of the ring oscillator is taken from one collector (node A) of l2L gate Q7 and applied to the base of transistor
08. The output of Q8 is applied to the base of l2L gate Q9 in the pulse generating circuit. The pulse generating circuit also includes transistors QlO, Qll, bias transistors Q14 and Q15, and pn junction capacitor C3.

   During operation, the pulse generating circuit generates a positive pulse at node C for each positive transi- tion at the output (node A) of the ring oscillator. Prior to the positive transition at node A, the voltages at n...