US 6,724,376 B2 · LED driving circuit and optical transmitting module

Abstract

An LED is an element in which when a voltage pulse applied to the intrinsic diode of an electrical equivalent model reaches a peak value, a current suddenly flows to obtain an optical output proportional to the forward current. By utilizing this property, the LED receives a rectangular voltage pulse having a large-current driving ability at a low output impedance, or a voltage pulse having two high levels. The low level of the voltage pulse is set within a voltage range where the extinction ratio of an output signal from the LED can be maintained. Even in an LED having a large internal capacitance, an increase in power consumption can be minimized, the transient response time can be shortened, high-speed modulation can be performed, and output light almost free from pulse waveform distortion can be obtained.

Claims28

Dependent claims

An LED driving circuit comprising:

a pulse generation circuit for shaping a waveform of an externally input signal and generating first and second pulses having a complementary relationship;
a first voltage transfer circuit for applying to an LED a first output voltage of a low level on the basis of the first pulse, and
a second voltage transfer circuit for applying to the LED a second output voltage of a high level on the basis of the second pulse,
wherein the high level is substantially equal to a froward voltage for generating a forward peak current of the LED necessary for outputting light of a predetermined intensity from the LED,
the low level is substantially equal to a voltage for changing an emission intensity of the LED to zero or a negligible value, and
a real part of an output impedance of said pulse generation circuit is smaller than an internal series resistance of the LED.

3 more elements

An LED driving circuit comprising:

a voltage generation circuit for generating a first output voltage of low level, a second output voltage of first high level, and a third output voltage of second high level which is higher than the first high level;
a first MOS switch for transferring the first output voltage to an output terminal;
a second MOS switch for transferring the second output voltage to the output terminal;
a third MOS switch for transferring the third output voltage to the output terminal;
and
a pulse generation circuit for shaping a waveform of an externally input signal and generating first, second, and third rectangular pulses,
wherein an LED is electrically connected to the output terminal,
the first rectangular pulse is input to a gate of said first MOS switch,
the second rectangular pulse is input to a gate of said second MOS switch,
the third rectangular pulse is input to a gate of said third MOS switch,
after the third rectangular pulse changes to high level, the second rectangular pulse successively changes to a high level,
a level of the first rectangular pulse has a complementary relationship with a level (ORed level) obtained by ORing the second and third rectangular pulses, and
a high-level voltage applied to the LED is binary.

10 more elements

Dependencies are inferred from the claim text.

LED driving circuit and optical transmitting module

Life of this patent

LED driving circuit and optical transmitting module

Life of this patent

Abstract

Claims28