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Current Switching in ADC Systems

IP.com Disclosure Number: IPCOM000094684D
Original Publication Date: 1965-Apr-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Ottesen, H: AUTHOR

Abstract

Analog voltages are generated by a ladder network. In such circuits, a required voltage is generated by supplying current to selected points in the network. Thus, current switches are required. This circuit is a current switch in which the current supply is actually switched on and off rather than by steering the current either to the ladder or to ground.

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Current Switching in ADC Systems

Analog voltages are generated by a ladder network. In such circuits, a required voltage is generated by supplying current to selected points in the network. Thus, current switches are required. This circuit is a current switch in which the current supply is actually switched on and off rather than by steering the current either to the ladder or to ground.

The circuit has three transistors T1, T2 and T3. Transistor T2 is connected in the inverted mode and it is turned on and off by the drive pulse through transistor T3. Changing the state of transistor T2, in turn, switches transistor T1, thus turning the current to the ladder network on or off.

Since T2 is operated in the inverted mode, the saturation voltage is small. By properly adjusting RA and E, the saturation voltage of transistor T2 can be made less than one millivolt. When a negative voltage is applied to the input terminal, transistor T3 turns on. T2 turns off and IC is substantially zero. When the input is grounded, T3 turns off, T2 turns on and IC turns on. When transistor T2 is on, it is driven by a base current equal to E/RA. RA can be selected so that the emitter to collector voltage of transistor T2 is less than a millivolt. Hence, V is transferred to the emitter of T2 and current flows through T1 to the ladder network.

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