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Photoamplifier With Self Adjusting Threshold For Symmetrical Output Pulses

IP.com Disclosure Number: IPCOM000048805D
Original Publication Date: 1982-Mar-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Goldrian, G: AUTHOR [+2]

Abstract

Printers use optical transducers for deriving timing information for electrode firing. Generally, firing pulses are generated only from one transition in the optical channel, using, for example, the bright-dark transition. The dark-bright transition is not used because the timing between the two transitions is not sufficiently accurate. The circuitry described permits using both transitions, thus reducing the number of marks on the circumference of the optical disk by a factor of two. As a result, the light intensity on the phototransistor is increased and the noise sensitivity decreased. The duty cycle of the comparator output voltage is measured and used to adjust the compare voltage, so that there is always a duty cycle of 50 percent.

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Photoamplifier With Self Adjusting Threshold For Symmetrical Output Pulses

Printers use optical transducers for deriving timing information for electrode firing. Generally, firing pulses are generated only from one transition in the optical channel, using, for example, the bright-dark transition. The dark-bright transition is not used because the timing between the two transitions is not sufficiently accurate. The circuitry described permits using both transitions, thus reducing the number of marks on the circumference of the optical disk by a factor of two. As a result, the light intensity on the phototransistor is increased and the noise sensitivity decreased. The duty cycle of the comparator output voltage is measured and used to adjust the compare voltage, so that there is always a duty cycle of 50 percent.

Amplifier Al is used to convert the current of phototransistor PTX into a voltage. Diode GA with a parallel resistor ensures a non-linear transfer characteristic for the amplifier with higher amplification at lower amplitudes. This characteristic is used to compensate for the non-linearity of the phototransistor.

Comparator Cl is used to derive a digital signal from the output voltage of amplifier Al. This signal serves to generate the firing pulses for the electrodes. The output voltage of amplifier A1 is compared with a reference voltage consisting of two components, the first of which is derived from a fixed divider and the second from the output of amp...