Browse Prior Art Database

Pseudo Schottky Output Driver

IP.com Disclosure Number: IPCOM000061811D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Hurd, JJ: AUTHOR [+2]

Abstract

A circuit is added to an open collector driver on a chip without any Schottky barrier diodes to enable faster switching without a Schottky diode. In its simplest form, an open collector driver is rather slow acting due to saturation of its transistor so that it cannot be used where the frequency is much greater than 2 MHz. This long turn-off delay of the transistor can be reduced by adding a Schottky diode between the base and collector of the transistor to prevent it from saturating. However, with a chip having no Schottky barrier diodes, this is not available. A chip 1 includes an NPN transistor 2, which must be turned off and on at a frequency of at least 4 MHz and is the transistor of the simplest form open collector driver that saturates. The chip 1 has a constant current source 3 controlled by a switch 4.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 66% of the total text.

Page 1 of 2

Pseudo Schottky Output Driver

A circuit is added to an open collector driver on a chip without any Schottky barrier diodes to enable faster switching without a Schottky diode. In its simplest form, an open collector driver is rather slow acting due to saturation of its transistor so that it cannot be used where the frequency is much greater than 2 MHz. This long turn-off delay of the transistor can be reduced by adding a Schottky diode between the base and collector of the transistor to prevent it from saturating. However, with a chip having no Schottky barrier diodes, this is not available. A chip 1 includes an NPN transistor 2, which must be turned off and on at a frequency of at least 4 MHz and is the transistor of the simplest form open collector driver that saturates. The chip 1 has a constant current source 3 controlled by a switch 4. A voltage source 5, which is off the chip 1 as is a resistor 6, is connected to a pad 7 of the chip 1 through the resistor 6. When the switch 4 is closed, nearly all of the 150 microamps of current from the current source 3 flows through a resistor 8 since the base current of an NPN transistor 9 is negligible. Since both the transistors 2 and 9 are forward biased, the voltage at a node 10 will be 2 VBE (voltage base emitter) above ground. Since VBE =
0.7 volts, the node 10 is 1.4 volt above ground. With the resistor 8 having a resistance of 3K ohms, the voltage drop across the resistor 8 will be 300 mV. Accordingly, the voltag...