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Sample and Hold Circuit

IP.com Disclosure Number: IPCOM000092766D
Original Publication Date: 1967-Jan-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Schulz, RA: AUTHOR

Abstract

When the sample pulse is applied to switched current sink 10, transistorized differential amplifier 11 is turned on and the sampling circuit acts as a conventional operational amplifier. Storage capacitor 12 is charged through current source 13 and current sink 14 to a voltage level necessary to make its output voltage equal to the input voltage within the accuracy of amplifier 11. When the sample pulse is removed, amplifier 11 is shut off, turning off source 13 and sink 14. The output buffer 15 is a high input impedance, low leakage stage. Buffer 15 has a DC offset of less than the voltage across either of the forward biased, clamping diodes 18 and 19. Thus, the voltage being held by capacitor 12 is approximately equal to the output voltage.

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Sample and Hold Circuit

When the sample pulse is applied to switched current sink 10, transistorized differential amplifier 11 is turned on and the sampling circuit acts as a conventional operational amplifier. Storage capacitor 12 is charged through current source 13 and current sink 14 to a voltage level necessary to make its output voltage equal to the input voltage within the accuracy of amplifier 11. When the sample pulse is removed, amplifier 11 is shut off, turning off source 13 and sink 14. The output buffer 15 is a high input impedance, low leakage stage. Buffer 15 has a DC offset of less than the voltage across either of the forward biased, clamping diodes 18 and 19. Thus, the voltage being held by capacitor 12 is approximately equal to the output voltage. Output terminal 17 becomes a low impedance point which is used as a floating clamp for diodes 18 and 19.

By connecting the feedback loop from output 17 through resistor 16 to the input of amplifier 11, possible breakdown of the transistorized base-emitter junctions of amplifier 10 is prevented by attenuation when a reverse polarity signal is applied where a large voltage is being held.

Hold-off current sources 20 and 21 conduct through diodes 18 and 19, reverse biasing holding diodes 22 and 23 that isolate capacitor 12. Each diode 22 and 23 is reverse biased by approximately the forward drop across diodes 18 and 19. Under such condition, the reverse bias of diodes 22 and 23 is very small and is indepe...