Open-Loop Transimpedance Amplifier for Infrared Diodes

Abstract

A microcontroller integrated circuit includes an open-loop transimpedance amplifier (OLTA). An input lead of the OLTA is a terminal of the microcontroller. The cathode of a photodiode is connected to VDD and the anode is connected to the terminal. The OLTA maintains the photodiode in a strongly reverse-biased condition, thereby keeping diode capacitance low and facilitating rapid circuit response. The input of the OLTA involves a diode-connected field effect transistor that provides a low impedance. This low impedance decreases as the diode current increases, thus providing effective clamping of the voltage on the terminal. By this clamping, the amount of photodiode capacitance discharging necessary when transitioning from a high input current condition to a low input current condition is reduced, thereby further improving amplifier response time. The OLTA is small and consumes less than thirty microamperes and functions to mirror photodiode current and compare to a predetermined level.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]This application is a continuation of, and claims priority under 35 U.S.C. §120 from, nonprovisional U.S. patent application Ser. No. 11 / 479,037 entitled “Open-Loop Transimpedance Amplifier for Infrared Diodes,” filed on Jun. 30, 2006, now U.S. Pat. No. ______ the subject matter of which is incorporated herein by reference.TECHNICAL FIELD[0002]The described embodiments relate to infrared receiver circuits, and more particularly to an infrared receiver circuit that is fully integrated onto a microcontroller integrated circuit within a learning remote control device.BACKGROUND INFORMATION[0003]Manufacturers of electronic consumer devices (for example, televisions, radio tuners, home theatre and entertainment systems, digital video disc (DVD) players, video cassette recorders (VCR), compact disc (CD) players, set-top cable television boxes, set-top satellite boxes, video game controllers, home appliances, etc.) typically supply an infrared re...

AI Technical Summary

Benefits of technology

[0011]The OLTA includes a diode-connected N-channel transistor circuit as an input stage. The diode-connected N-channel transistor circuit biases the voltage on the input terminal under dark conditions (photodiode not activated by light) at approximately one N-channel transistor Vt (threshold voltage) above ground potential. Because the cathode of the photodiode is coupled to VDD and the anode is coupled to the input terminal, the photodiode is biased in a strongly reverse-biased condition. Keeping the photodiode strongly reverse-biased minimizes the parasitic capacitance of the photodiode and thereby facilitates fast response times of the OLTA.

Problems solved by technology

In addition, the user may have to power on and control the television with a second remote control device that issues operational signals that the television responds to.

The infrared receiver circuit is typically a fairly expensive circuit that consumes a substantial amount of power when it is functioning.

If either of these traditional infrared receiver circuits were to be integrated into the microcontroller integrated circuit, then the resistors and capacitors and / or the complex operational amplifier circuitry would consume an undesirably large amount of die area, thereby increasing the cost of the microcontroller integrated circuit.

Accordingly, integrating an infrared receiver circuit onto a microcontroller integrated circuit that is to see general usage in non-learning remote control devices can be recognized to be unacceptably expensive.

Moreover, the hundreds of microamperes of power consumed by such a traditional infrared receiver would be undesirable.

In addition, the photodiode in a learning remote control device involves a parasitic capacitance.

Ordinary amplifier circuits used in learning remote control devices to amplify photocurrents can have significant input impedances and can therefore be slow in discharging the photodiode's parasitic capacitance, thereby contributing to slow response times.

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