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Control Circuit for Sample And Hold Devices

IP.com Disclosure Number: IPCOM000088057D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Delarue, J: AUTHOR [+3]

Abstract

Fig. 1a shows a sample-and-hold device which comprises a first operational amplifier OP1 receiving on terminal I1 the analog input to be sampled, a second operational amplifier OP2 and holding capacitor C. The first amplifier acts as a switch controlled by a sampling signal.

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Control Circuit for Sample And Hold Devices

Fig. 1a shows a sample-and-hold device which comprises a first operational amplifier OP1 receiving on terminal I1 the analog input to be sampled, a second operational amplifier OP2 and holding capacitor C. The first amplifier acts as a switch controlled by a sampling signal.

Fig. 1b shows amplifier OP1 and a switching control circuit which allows the switching time of amplifier OP1 to be minimized. Terminals I1, I2, Control and A are represented in Fig. 1b, and holding capacitor C and buffering circuit OP2 have to be connected to these terminals, as shown in Fig. 1a.

The switching control circuit comprises an arrangement of transistors T1, T2 and T3 with their associated resistors R1, R2 and R3, and diodes D2 and D3. Operational amplifier OP1 comprises transistors T4 to T11.

When the control signal is at its high level + V(CC), transistors T1, T3 and T7 are conducting. Diodes D2 and D3 are reverse-biased while diode D4 is forward- biased. Thus, the switching circuit OP1 is ON. When the control signal is at its low level, diodes D2 and D3 turn on very fast and diode D4 becomes reverse- biased. Consequently, the switch is OFF since the current flows into diodes D2 and D3 instead of flowing in transistors T10 and T11. Transistors T1, T3 and T7, having a response time shorter than that of diodes D2 and D3, become nonconducting and no current flows in the switch.

Diode D4 prevents the control circuit from affecting node A. W...