Browse Prior Art Database

HIGH VOLTAGE BiCMOS SWITCH AND LEVEL TRANSLATOR

IP.com Disclosure Number: IPCOM000008104D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-17
Document File: 3 page(s) / 129K

Publishing Venue

Motorola

Related People

Joseph Charaska: AUTHOR

Abstract

The circuit presented is a high speed, level translating switch to be used to operate a charge pump of a synthesizer. The charge pump circuitry, with can operate from a five volt supply, is con- trolled by signals which are produced by CMOS logic operating from a three volt supply. To accom- plish this, a high speed switch was designed. The switch accepts a 3 volt control signals and produces control signals at a higher voltage without damage to the gate oxide. This is necessary since the gate oxide of the 0.5um BiCMOS process can only with- stand 3.6 volts without degradation or failure.

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0 M MO-LA

Technical Developments

HIGH VOLTAGE BiCMOS SWITCH AND LEVEL TRANSLATOR

by Joseph Charaska

ABSTRACT

  The circuit presented is a high speed, level translating switch to be used to operate a charge pump of a synthesizer. The charge pump circuitry, with can operate from a five volt supply, is con- trolled by signals which are produced by CMOS logic operating from a three volt supply. To accom- plish this, a high speed switch was designed. The switch accepts a 3 volt control signals and produces control signals at a higher voltage without damage to the gate oxide. This is necessary since the gate oxide of the 0.5um BiCMOS process can only with- stand 3.6 volts without degradation or failure.

INTRODUCTION

  The Offset Direct Conversion Transmitter inte- grated circuit (ODCT IC) is a key component of the next generation of the iDEN subscriber transmitter integrated circuit chip set. The ODCT IC is designed using Motorola's 3 Volt BiCMOS85 process (0.5 um). The gate oxide thickness of this process limits the maximum voltage across the gate oxide to 3.6 volts. This means the voltage from gate to source, gate to drain, or gate to body of the MOS transistors can not exceed 3.6 volts without reducing the MOSFET reliability or causing oxide failure.

  Most of the circuitry in the ODCT IC is designed to operate from a 3 volt supply, except for part of the frequency synthesizer. The charge pump, which drives the steering line of the external volt- age controlled oscillator (VCO) is designed to oper- ate over an extended voltage supply range (2.7 volts to 5.5 volts). This will allow the steering line of the VCO to operate at the higher supply voltage were the sideband noise of the VCO can be optimized in the product. In the future, as the VCO resonator technology continues to advance and production variations are reduced, the charge pump voltage can

be reduced to 2.7 volts. To avoid a redesign in the future, the charge pump design can accommodate the full supply range (2.7 volts to 5.5 volts).

CHARGE PUMP CONTROL OPERATION (REFER TO FIGURE 1 AND FIGURE 2)

  For reasons of sideband noise, only the charge pump circuit is to operate over an extended supply range. To protect the MOSFET devices in the charge pump circuit from excessive voltage across the gate oxide, cascaded MOSFET devices or guard devices [devices 3, 4, 5, 61 are used with their gate terminals biased near one half of the supply voltage. This technique was also used to reduce the occu...