Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Utility Patent
1999-05-17
2001-01-02
Nelms, David (Department: 2818)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S108000, C327S543000
Utility Patent
active
06169445
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to transmitters and more particularly pertains to a new current mode transmitter for driving an infrared light emitting diode with an output current which follows very closely an associated input pulse.
2. Background Art
Known prior art transmitters include the circuit shown in FIG.
1
. As shown, a controlled switch such as a transistor is connected to a ballast resistor. As is conventional, an infrared light emitting diode is connected between the ballast resistor and a voltage supply. In use, the switch is opened and closed in order to effect the transmission of light by the infrared light emitting diode. While the switch is closed and the infrared light emitting diode is illuminated, the resistor serves for limiting an amount of current that passes through the infrared light emitting diode. Due to the necessity of such resistor, a voltage supply in the order of 5V is required so that a sufficient voltage drop is present across the infrared light emitting diode. A problem thus arises when a reduced voltage supply of about 3.3V is desired. With this reduced voltage, an inadequate voltage drop is present across the infrared light emitting diode and the necessary presence of the resistor becomes problematic due to difficulties in tolerating the infrared light emitting diode forward voltage, supply voltage tolerance, and ambient temperature.
In these respects, the current mode transmitter according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed for the purpose of driving an infrared light emitting diode with an output current instead of a voltage as is the case in prior art devices.
SUMMARY OF THE INVENTION
In view of the foregoing disadvantages inherent in the known types of transmitters now present in the prior art, the present invention provides a new current mode transmitter circuit wherein the same can be utilized for driving an infrared light emitting diode with an output current which follows very closely an associated input pulse.
To attain this, a current mode transmitter is provided that includes a charge circuit connected to an enable node and adapted to generate a charge current upon the receipt of an activation signal at the enable node. Also included is a discharge circuit connected to the enable node and adapted to generate a discharge current upon the cessation of the receipt of the activation signal at the enable node. An output circuit is connected between an output node and the charge and discharge circuits. The output circuit serves for generating an output current at the output node in response to the charge current and the discharge current. Such output current is initiated within a first delay after the detection of the activation signal by the charge circuit. Further, the output current is terminated within a second delay after the detection of the cessation of the receipt of the activation signal by the discharge charge circuit. The first delay and the second delay are substantially similar such that a pulse width of the output current is substantially similar to a pulse width of the activation signal received at the enable node. The output current may thus be used to drive an infrared light emitting diode with very fast rise and fall times while maintaining tight control over the pulse width of the output current.
REFERENCES:
patent: 5568084 (1996-10-01), McClure et al.
Hickman Coleman & Hughes LLP
Lam David
Maxim Integrated Products Inc.
Nelms David
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