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Output Driver With Controlled Rise/Fall Times

IP.com Disclosure Number: IPCOM000062683D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Klein, W: AUTHOR [+3]

Abstract

An emitter follower output driver is proposed, the slew rate of which can be arbitrarily adjusted. For that purpose, the input of the output driver is provided with a capacitor which is charged via a first constant current source and discharged via a second constant current source. The desired slew rate is obtained by suitably dimensioning the two constant current sources. The figure shows a circuit diagram. Capacitor C at the input of the circuit is charged by current IC of the first constant current source 1. Current ID of the second constant current source 2, which comprises a difference amplifier T3, T4, controlled by a read amplifier (not shown), discharges capacitor C. If current ID = 2 x IC, the leading and the trailing edge are equal.

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Output Driver With Controlled Rise/Fall Times

An emitter follower output driver is proposed, the slew rate of which can be arbitrarily adjusted. For that purpose, the input of the output driver is provided with a capacitor which is charged via a first constant current source and discharged via a second constant current source. The desired slew rate is obtained by suitably dimensioning the two constant current sources. The figure shows a circuit diagram. Capacitor C at the input of the circuit is charged by current IC of the first constant current source 1. Current ID of the second constant current source 2, which comprises a difference amplifier T3, T4, controlled by a read amplifier (not shown), discharges capacitor C. If current ID = 2 x IC, the leading and the trailing edge are equal. At ID > 2 x IC, the trailing edge is steeper than the leading one, whereas at ID < 2 x IC, the leading edge is steeper than the trailing one. The voltage curve at node IN is transferred by means of transistors T7 and T8 and constant current source T9 to the base of emitter follower TU and thus to output pad DO. Circuit stability is obtained by connecting the emitters of transistors T7 and T8 to current source T9 via resistor RS. To prevent the driver from being interfered with through output pad DO, the transfer function of T7, T8, T9 is effective only during switching. For that purpose, the output level at output pad DO is limited to -0.9 and -2.1 V, respectively, while the inpu...