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Peak Loop Circuitry for Infrared Processing of Encoded Data

IP.com Disclosure Number: IPCOM000039401D
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 64K

Publishing Venue

IBM

Related People

Munoz-Bustamante, C: AUTHOR [+3]

Abstract

A technique is described whereby receiving infrared transmitted data, as used in local area network (LAN) packet applications, is enhanced through the use of a "Peak Loop" circuit. The circuit is designed to reduce bit errors by minimizing undesirable noise, such as "jitter", caused by long wait states associated with the processing of data code. Threshold system circuits, typically used as receiving schemes to increase the signal sensitivity for decoding infrared packet LAN information, usually consist of one of the following concepts: - Adaptive Hysteresis - The threshold level is automatically adjusted as a function of signal strength. - Automatic Gain Control (AGC) - The signal strength is automatically adjusted as a function of the threshold values.

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Peak Loop Circuitry for Infrared Processing of Encoded Data

A technique is described whereby receiving infrared transmitted data, as used in local area network (LAN) packet applications, is enhanced through the use of a "Peak Loop" circuit. The circuit is designed to reduce bit errors by minimizing undesirable noise, such as "jitter", caused by long wait states associated with the processing of data code. Threshold system circuits, typically used as receiving schemes to increase the signal sensitivity for decoding infrared packet LAN information, usually consist of one of the following concepts: - Adaptive Hysteresis - The threshold level is

automatically adjusted as a function of signal

strength.

- Automatic Gain Control (AGC) - The signal strength

is automatically adjusted as a function of the

threshold values.

- Simple Threshold - The lowest cost scheme, but has

sensitivity and dynamic range problems.

(Image Omitted)

The adaptive hysteresis and the AGC approach

are considered the best circuit approach to

provide automatic adjustments of the signal.

There are four distinct parameters which must be

taken into consideration: jitter, guard time at

the end of the packet, sensitivity and dynamic

range. Typically, a trade-off is needed whereby

the two approaches will provide low noise jitter

at the expense of a long guard time at the end of

the packet. Conversely, a short guard time will

cause a high jitter. The circuit described herein

eliminates this trade-off of jitter and guard

time, while still providing both low AGC droop and

a very short guard time. An example of the trade-off between guard time and jitter for an infrared coded packet being received by an AGC circuit is shown in Fig. 1. A typical infrared packet has preamble 1, followed by start code violation 2, followed by data 3, followed by end code violation or delimiter 4. Jitter 5 is shown increasing due to the use of a fast AGC decay time 6 so that the guard time can be decreased. Jitter 7 is shown decreasing through the use of a slow AGC decay time 8 and a longer guard time 9, so as to minimize jitter. Note that a long guard time is undesirable, since the entire LAN will not be transmitted during the guard time. To eliminate the trade-off of jitter and guard time, a peak loop circuit was designed, as shown in Fig. 2. The circuit consists of optical front end 10, preamplifier 11, second stage amplifier with internal AGC circuitry 12, comparator 13, gate array 14 to control the sign...