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Browse Prior Art Database

Spectrophotometric Clocking Circuit

IP.com Disclosure Number: IPCOM000089306D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 41K

Publishing Venue

IBM

Related People

Minikel, H: AUTHOR

Abstract

Some types of spectrophotometers use circular variable filters along with timing wheels. The filters convert polychromatic light into monochromatic light, and the timing wheels cause pulses to be generated that are indicative of the angular position of the filter and hence of the wavelength being transmitted by the filter. Such instruments normally employ ADCs (analog-to-digital converters) for converting the output of a detector, which produces an output proportional to the intensity of the light being received thereby, into a digital form useful in analyzing the signals. In such instruments, it is desirable to be able to synchronize the ADC to the timing pulses. Shown in the drawing is a circuit for accomplishing such a function.

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Spectrophotometric Clocking Circuit

Some types of spectrophotometers use circular variable filters along with timing wheels. The filters convert polychromatic light into monochromatic light, and the timing wheels cause pulses to be generated that are indicative of the angular position of the filter and hence of the wavelength being transmitted by the filter. Such instruments normally employ ADCs (analog-to-digital converters) for converting the output of a detector, which produces an output proportional to the intensity of the light being received thereby, into a digital form useful in analyzing the signals. In such instruments, it is desirable to be able to synchronize the ADC to the timing pulses. Shown in the drawing is a circuit for accomplishing such a function.

Assume that a timing wheel and filter rotate at a speed of five revolutions per second and that the timing wheel provides a pulse each one degree of revolution. By using a 4 megahertz oscillator and recognizing that the timing pulses may be out of phase with those coming from the oscillator, a resolution of 250 nanoseconds is obtainable by the illustrated circuit. Assume also that the logic blocks are implemented in a TTL (transistor-transistor logic) technology and operate at the speed thereof. The 1 Degrees pulse is simultaneously applied to an AND circuit 10, to the set input of a FL (flip latch) 11 and to an inverter 12. The input to the circuit is a 1 Degrees timing pulse having the waveform illustrated at (a). The purpose of the circuit is to generate a Start Convert signal (shown at (b)) on line 13 which signal is used by the ADC to initiate conversion and to generate a 500 kilohertz pulse on line 14 for controlling the rate of conversion.

At the start of the 1 Degrees pulse, the positive transition coupled with a positive pulse from oscillator 17 causes AND circuit 10 to produce a negative output that resets FL 11. The output of FL 11 is thus turned positive and is applied to the reset input of a count...