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A TTL COMPATIBLE RF SWITCH TOPOLOGY FOR GaAs MMIC APPLICATIONS

IP.com Disclosure Number: IPCOM000006672D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2002-Jan-22
Document File: 2 page(s) / 85K

Publishing Venue

Motorola

Related People

W. L. Seely: AUTHOR [+3]

Abstract

Some of the earliest successful C&As MMIC cir- cuits include RF switches, which form one of the basic building blocks used in RF and microwave systems. However, GaAs switch control inputs range from 0 to -3 volts. TTL control logic ranges from 0 to +5 volts. Thus, a separate driver circuit has been required to inter- face between the switch and the TfL logic circuits. This separate driver circuit consumes power, increases con- trol propagation times, adds substantial circuitry which affects reliability, increases semiconductor area, and atfects product cost. This article describes a method of realiz- ing a TTL compatible GaAs MMIC RF switch, completely eliminating the requirements for a separate driver.

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INC. Technical Developments Volume 17 December 1992

A TTL COMPATIBLE RF SWITCH TOPOLOGY FOR GaAs MMIC APPLICATIONS

by W. L. Seely, J. M. Golio and M. B. Davis

  Some of the earliest successful C&As MMIC cir- cuits include RF switches, which form one of the basic building blocks used in RF and microwave systems. However, GaAs switch control inputs range from 0 to -3 volts. TTL control logic ranges from 0 to +5 volts. Thus, a separate driver circuit has been required to inter- face between the switch and the TfL logic circuits. This separate driver circuit consumes power, increases con- trol propagation times, adds substantial circuitry which affects reliability, increases semiconductor area, and atfects product cost. This article describes a method of realiz- ing a TTL compatible GaAs MMIC RF switch, completely eliminating the requirements for a separate driver.

  The basic switch topology is shown in Figure 1. It consists of a gate grounded depletion mode MESFET 13 with resistors 14 and 15 from both the source and drain to a common control node 19. DC blocking capac- itors 11 and 12 are included to contime the applied volt- ages to the MFSFET. RF energy applied across the source and drain can be switched between a low loss state and a high loss state merely by changing the control voltage level. With +5 volts applied to the control port, the MESFET looks like a high impedance. With the control level set to 0 volts, the MESFET is driven into a highly saturated state, where it looks like a very low imped- ance, In both cases there is no current flow other than leakage and/or capacitor charging currents. These volt-...