Browse Prior Art Database

Analog Switch

IP.com Disclosure Number: IPCOM000075420D
Original Publication Date: 1971-Sep-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Buhler, OR: AUTHOR

Abstract

This analog switch combines a bipolar transistor 10 and an N-channel depletion mode field-effect transistor 11 in a manner to reduce a low-level analog input signal voltage to the lower level of the inherent bipolar offset voltage, whereupon the low-resistance zero-offset characteristic of the FET is effective to determine the input-output characteristic of the switch. For large input signals, the circuit operates on the superior large signal characteristics of the bipolar switch. For small input signals, the circuit operates on the superior small signal characteristics of the FET switch.

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Analog Switch

This analog switch combines a bipolar transistor 10 and an N-channel depletion mode field-effect transistor 11 in a manner to reduce a low-level analog input signal voltage to the lower level of the inherent bipolar offset voltage, whereupon the low-resistance zero-offset characteristic of the FET is effective to determine the input-output characteristic of the switch. For large input signals, the circuit operates on the superior large signal characteristics of the bipolar switch. For small input signals, the circuit operates on the superior small signal characteristics of the FET switch.

The analog switch, Fig. 1, includes PNP transistor 10 and FET 11 which are simultaneously switched to conductive or nonconductive states by a switching network 12, the details of which are shown in Fig. 2. The input signal voltage "E in" is a reversible polarity DC voltage. When the transistor and the FET are turned on, the voltage level of junction 13 assumes a low level as determined by the inherent offset of the transistor. This offset is a function of transistor current flow and thus is a function of the value of resistor 14. This low-level voltage at junction 13 is again switched by resistor 15 and the conducting FET.

For large input signals, the transistor switches "E in" to a lower level at 13 than that which is determined by the FET characteristic. This voltage is then attenuated again by resistor 15 and the FET.

For small input signals, the transistor swit...