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# Analog To Digital Frequency Measuring System

IP.com Disclosure Number: IPCOM000093842D
Original Publication Date: 1966-Mar-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 5 page(s) / 79K

IBM

## Related People

Yeager, AP: AUTHOR

## Abstract

This system measures the frequency difference between two signals A and B having variable frequencies fa and fb. The system measures small frequency differences between two high-frequency signals.

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Analog To Digital Frequency Measuring System

This system measures the frequency difference between two signals A and B having variable frequencies fa and fb. The system measures small frequency differences between two high-frequency signals.

Successive cycles of signal A are in a given sequence such as, for example, cycle types a1...a4, a1...a4, etc., respectively, in drawing B. Certain cycles of signal B are designated b1 cycle types and are utilized to sample signal A. A predetermined, fixed integral of signal B cycles between b1 cycle types is provided, compatible to the system requirement. In the example, the b1 cycle types correspond to the 1st, 9th, 17th, etc., cycles of signal B.

Basically, at any given time, the system is, for example, in only one of four predetermined conditions c1...c4, respectively. Each condition sets the system to be only responsive to two predetermined cycle types of signal A when the latter is being sampled by signal B. If a predetermined one of these two cycle types is present in signal A for the particular condition when sampled by signal B, then the system is sequenced to the succeeding condition c1...c4. Note the upper portion of Table 1. If, however, the other type is present, the other circumstances being the same, then the system is sequenced to the preceding condition of the sequence. Note the lower portion of Table 1. The latter shows the two cycle type pairs in column II associated with the present corresponding condition in column 1 and their respective subsequent conditions in column III to which the system is sequenced.

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The arrangement is based on the principle that if fa is greater than fb, the signal A cycles are sampled by b1 cycle types in recurring progressive sequences, such as either the progressive sequence a1, a2, a3, a4 or the progressive sequence a4, a1, a2, a3, etc. However, if fa is less than fb, the signal A cycles are sampled by b1 pulses in a recurring reverse sequence, such as either the reverse sequence a4, a3, a2, a1 or a3, a2, a1, a4, etc. Under this arrangement, the system provides an output signal every time there is a change in condition. For a given set of input signal frequencies, if the system is in a condition that causes it to be incorrectly sequenced, the arrangement inherently causes the system to be subsequently, correctly sequenced. The interval between two successive output signals which are derived from two successive, correct sequences is proportional to the frequency difference between signals A and B.

When the frequencies of signals A and B are equal, sampling cycles b1 are locked on to a predetermined cycle type of signal A. When this happens, the system can be in a condition that is not associated with this particular cycle type of signal A. In this case, the system provides no output signal. Alternatively, when this happens, the system can be in a condition that is associated with this particular cycle type of signal A. In this cas...