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Corrective Duty-Cycle Decoder for Infrared Manchester Data Transmission

IP.com Disclosure Number: IPCOM000061614D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Zalph, W: AUTHOR [+3]

Abstract

This article describes a waveform duty cycle reconstruction circuit arrangement for infrared (IR) data transmission utilizing the Manchester data encoding method. However, it is not limited to use with Manchester but can be used with other encoding schemes. Manchester encoding can be used for IR data transmission. Manchester has a 50%/50% duty cycle with one transition in the middle of each bit cell. A positive transition denotes a logical 0, a negative transition denotes a logical 1. IR data transmission through the air with a 50%/50% duty-cycle will not be received in all places with a 50%/50% duty cycle. Duty-cycle degradation is caused by ever-decreasing signal-to-noise (S/N) ratios of the transmitted signal as a function of transmitter-to-receiver distance.

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Corrective Duty-Cycle Decoder for Infrared Manchester Data Transmission

This article describes a waveform duty cycle reconstruction circuit arrangement for infrared (IR) data transmission utilizing the Manchester data encoding method. However, it is not limited to use with Manchester but can be used with other encoding schemes. Manchester encoding can be used for IR data transmission. Manchester has a 50%/50% duty cycle with one transition in the middle of each bit cell. A positive transition denotes a logical 0, a negative transition denotes a logical 1. IR data transmission through the air with a 50%/50% duty-cycle will not be received in all places with a 50%/50% duty cycle. Duty-cycle degradation is caused by ever-decreasing signal-to-noise (S/N) ratios of the transmitted signal as a function of transmitter-to-receiver distance. The S/N ratio of the signal decreases as a function of distance, because the noise is essentially constant. The circuit arrangement disclosed herein converts the degraded waveform back to valid Manchester 50%/50% form. The circuit can correct signals as distorted as 5%/95% or 95%/5% back to a 50%/50% duty cycle. Prior-art waveform reconstruction schemes based on sampling techniques could at best reconstruct a 75%/25% or 25%/75% duty cycle degraded signal back to 50%/50% at 1 M/bit data rate. This is because of speed limitations of digital logic. A duty cycle reconstruction circuit improves noise immunity of data transfer and increases distance of IR data transmission. Fig. 1 shows the present circuit arrangement which accomplishes the conditional transfer chart logic of Fig. 2 and the table set forth at the end of the article. In thi...