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Integrate and Dump Infrared Receiver for Four-Slot Pulse Position Modulation Decoding

IP.com Disclosure Number: IPCOM000040172D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 70K

Publishing Venue

IBM

Related People

Bustamante, C: AUTHOR [+2]

Abstract

This article describes a circuit arrangement for a correlation detector which can be used for pulse position modulation (PPM) and is known as an "integrate and dump" receiver. It is known in the industry that a matched filter receiver is the optimum receiver for any given signal. A matched filter is one which has an impulse response which is the same as the signal waveform shape in the time domain. For example, a matched filter for a rectangular pulse is one that has a transfer function h(T) such that when an impulse function is convolved with h(T), the result is a rectangular pulse. A special case of a matched filter receiver for binary data is called a correlation detector. This is one where the ideal symbols for a "0" and a "1" are known and available in the detector.

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Integrate and Dump Infrared Receiver for Four-Slot Pulse Position Modulation Decoding

This article describes a circuit arrangement for a correlation detector which can be used for pulse position modulation (PPM) and is known as an "integrate and dump" receiver. It is known in the industry that a matched filter receiver is the optimum receiver for any given signal. A matched filter is one which has an impulse response which is the same as the signal waveform shape in the time domain. For example, a matched filter for a rectangular pulse is one that has a transfer function h(T) such that when an impulse function is convolved with h(T), the result is a rectangular pulse. A special case of a matched filter receiver for binary data is called a correlation detector. This is one where the ideal symbols for a "0" and a "1" are known and available in the detector. These symbols are synchronized with the data stream and multiplied, integrated, and sampled after integration. A special case correlation detector which can be used for PPM is called an integrate and dump receiver. Described herein are the circuits required to implement the integrate and dump concept for a PPM data stream.

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In a PPM encoding scheme, there is 1 pulse within a field of allowable pulse locations (time slots). Each location encodes a different data value. In the case of 4-slot PPM, 2 data bits are encoded. The PPM encoding method has its main advantage in its low duty cycle. This is important in the infrared media, as the transmission duty cycle has an effect on the temperature of the transmit diodes. Minimizing duty cycle and temperature of the diodes increases signal strength. The circuits, disclosed herein, implement integrate and dump as a subset of correlation detection. With integrate and dump, there is one integrator which performs the transfer function g(T). The integrator is in charge of integrating the incoming signal for each time slot of the PPM data. After the integration has been accomplished for a time slot, the voltage value is transferred to a storage cap, the integrator is reset (charge is dumped), and an integration begins for the next time slot. The process continues for all 4 time slots and then a comparison is required to find the largest resultant integration value of all 4 time slots, without introducing an irrelevant reference as is done in comparator designs. To avoid intersymbol interference, the energy must be taken completely out of the integrators before the next pulse position can be evaluated, hence the name integrate and dump. Traditional receivers for any digital transmission media must have gain stages to amplify the weak signals, followed by a comparator to decide the digital state of the amplified data. The comparator compares the amplified signal to some arbitrary reference to decide whether the signal is greater than or less than the reference, thus deciding the digital state of the receiver signals. If the select...