Browse Prior Art Database

Bootstrapped FET Driver

IP.com Disclosure Number: IPCOM000085433D
Original Publication Date: 1976-Apr-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Lewis, SC: AUTHOR [+3]

Abstract

This field-effect transistor (FET) driver circuit is input rise time and output load insensitive and allows the output rise time to be faster than the input rise time, by internally bootstrapping the gate of the output driver. An output responsive latch circuit is used to gate the bootstrap circuit.

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Bootstrapped FET Driver

This field-effect transistor (FET) driver circuit is input rise time and output load insensitive and allows the output rise time to be faster than the input rise time, by internally bootstrapping the gate of the output driver. An output responsive latch circuit is used to gate the bootstrap circuit.

Initially, a precharge pulse PC charges the gates of transistors T4 and T8. The START pulse begins to charge the gates of transistors T2 and T3. Transistor T4 overdrives T3 keeping node N2 low. When node N1 approaches 2Vth+overdrive, node N4 is approaching 1Vth and T7 begins to turn on, discharging the gates of transistors T4 and T8.

Eventually T4 turns off but not until a sizeable voltage has been built up across capacitor C1. Transistor T3 then bootstraps its gate which is connected to the gate of T2. Transistor T1 now acts as an isolation device during this time. When the start pulse discharges, node N1 is also discharged and node N4 remains at VH, because of the capacitive load.

In addition, the circuit only utilizes the input voltage to VH-Vth. This allows the output rise time to be faster than the input rise time and accounts for the input insensitivity.

In conventional bootstrap drivers capacitor C1 would be connected across transistor T2 (the output device) instead of transistor T3. In that configuration, the gate of T2 is bootstrapped by the rising output voltage. In this driver, the gate of the output device is internally bootstrapped...