Browse Prior Art Database

High Sensitivity Edge Comparator

IP.com Disclosure Number: IPCOM000083858D
Original Publication Date: 1975-Aug-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Edwards, DB: AUTHOR [+2]

Abstract

In order to detect if two pulse edges are in synchronism, a circuit must be able to detect the time difference between them. A negative AND gate will do this if one signal is inverted as shown in Fig. 1.

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 100% of the total text.

Page 1 of 2

High Sensitivity Edge Comparator

In order to detect if two pulse edges are in synchronism, a circuit must be able to detect the time difference between them. A negative AND gate will do this if one signal is inverted as shown in Fig. 1.

The output of the NAND gate is used to set a latch which will indicate that the signals are not in synchronization. In order to detect differences in the fractions of nanoseconds region, the NAND gate must be very fast and the latch must be very sensitive which presents a problem of noise immunity. To overcome the noise problem, the two circuits are combined on the same chip using high-speed technology.

As shown in Fig. 2, the circuit is designed so that only a small change in voltage of about 50 mv at the collector of transistor T5 causes the latch T1, T2 and T6, T7 to set. A difference of only about 0.5 ns at the high-speed current switch bases of transistors T3 and T4 will cause a set signal to appear at the collector of T5.

The -1.5 V power supply is common to the collectors of the latch transistors and also the reference for the current switch. This makes noise spikes on the - 1.5 volt line common to both circuits, which prevents them from setting the latch. Noise on the -4.25 volt line is similarly rejected. Transistors T8 and T9 form the output stage and buffer the latch further from noise.

1

Page 2 of 2

2

[This page contains 3 pictures or other non-text objects]