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Low Power Counter for Electronic Watch

IP.com Disclosure Number: IPCOM000078527D
Original Publication Date: 1973-Jan-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Hill, CP: AUTHOR

Abstract

One of the prime goals in designing an electronic watch controlled by a quartz-crystal oscillator is to minimize power dissipation. The complementary metal-oxide silicon (CMOS) process for making field-effect transistors (FET's) has been used to provide very low-power circuits, from which binary counters are constructed. Using CMOS circuits, the power required in the binary counter is a function of the frequency with which each stage of the counter switches state.

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Low Power Counter for Electronic Watch

One of the prime goals in designing an electronic watch controlled by a quartz-crystal oscillator is to minimize power dissipation. The complementary metal-oxide silicon (CMOS) process for making field-effect transistors (FET's) has been used to provide very low-power circuits, from which binary counters are constructed. Using CMOS circuits, the power required in the binary counter is a function of the frequency with which each stage of the counter switches state.

In the conventional BCD counter with 15 stages to downconvert a 32,765 Hz signal to 1 Hz, the changes of state for the 15 flip-flop stages are as follows: Time

Interval S1 S2 S3 S4 . . . S15 1 Hz Output 0 0 0 0 0

1 1 0 0 0

2 0 1 0 0

3 1 1 0 0

4 0 0 1 0

5 1 0 1 0

6 0 1 1 0

7 1 1 1 0

8 0 0 0 1

Number of
State
Changes 8 4 2 1
Power per
Stage X X/2 X/4 X/8 . . . = 2x Total Power

By using the "Johnson Code" or "Creeping Code" at the front end of such a counter instead of the conventional code, the power requirement is reduced as illustrate: Time

Interval S1 S2 S3 S4 S5 . . . S15 1 Hz Output 0 0 0 0 0 0

1 1 0 0 0 0

2 1 1 0 0 0

3 1 1 1 0 0

4 1 1 1 1 0

5 0 1 1 1 0

6 0 0 1 1 0

7 0 0 0 1 0

8 0 0 0 0 1

Number of
State
Changes 2 2 2 2 1
Pwr x x x x x
Stage 4 4 4 4 8 = 1.25 X Total Power

This technique may be extended to effectively reduce the power of dissipation in a long counter by in the limit of a factor of 2.

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