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Predriver Level Shifter for Infrared Transmitter

IP.com Disclosure Number: IPCOM000039243D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Bustamante, C: AUTHOR [+2]

Abstract

This article describes a circuit arrangement for a predriver level shifter for a power field-effect transistor (FET). This circuit takes a logic signal from a transceiver gate array and converts the signal to low impedance 12-volt logic levels to drive a power FET which acts as a current sink to drive an infrared (IR) light-emitting diode (LED) bank. Switching the LED bank as fast as possible is important because of the receiver filtering method. The receiver, in order to filter out high frequency fluorescent bulb noise, utilizes three filters of differentiation. The output signal voltage of the receiver is a strong function of the rise time of the received signal.

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Predriver Level Shifter for Infrared Transmitter

This article describes a circuit arrangement for a predriver level shifter for a power field-effect transistor (FET). This circuit takes a logic signal from a transceiver gate array and converts the signal to low impedance 12-volt logic levels to drive a power FET which acts as a current sink to drive an infrared (IR) light-emitting diode (LED) bank. Switching the LED bank as fast as possible is important because of the receiver filtering method. The receiver, in order to filter out high frequency fluorescent bulb noise, utilizes three filters of differentiation. The output signal voltage of the receiver is a strong function of the rise time of the received signal. The rise time of the received signal is controlled first by the switching characteristics of the transmitter, then by the bandwidth characteristics of the receiver. The significant characteristics at the transmitter are the switching speed of the transmit LEDs and the speed of the circuits which switch the LEDs. At the receiver, the characteristic which affects the received rise time is the high frequency roll-off. By minimizing the rise time at the receiver, the output signal amplitude after differentiation is maximized. The noise voltages inherent in the system are primarily caused by photo-diode shot noise and the front-end resistor thermal noise which both have a flat amplitude characteristic in the frequency domain. It is clear that these noise voltages are in no way a function of the received data rise time for a fixed amplifier bandwidth. Therefore, by minimizing the received data rise time, one has maximized the signal voltage after differentiation while noise voltage has remained constant. This means that minimizing the received data rise time maximizes the post-differentiation signal- to-noise ratio (S/N) and o...