Pulse shaping circuit

Abstract

The invention relates to a pulse shaping circuit for shaping electrical pulses driving an optical transmitter, e.g. a lased diode or an LED, and for providing electrical pulses having independently height and width-adjustable peaking at the edges thereof. The pulse shaping circuit of the present invention includes a high-pass RC filter with a differential output for providing transient electrical pulses from an input differential pulse, an adjustable voltage offset generating circuit, a differential amplifier for adjusting the width of the transient electrical pulses in dependence on the adjustable voltage offset, and a variable-gain current-steering amplifier for producing transient pulses with independently adjustable width and height.

Description

technical field [0001] [1] The present invention relates to a pulse shaping circuit, and in particular to a circuit for adding peaking with adjustable width and height to pulse edges. Background technique [0002] [2] In many applications, a light emitter such as a laser diode (LD) or light emitting diode (LED) is driven by a pulsed current to alternately turn on or off the light source and generate light pulses. [0003] [3] In general, it is desirable for the light pulse to have a roughly rectangular shape and to follow the current pulse as closely as possible. However, there is a time delay associated with switching on or off the light emitter, eg between a switching transition of the drive current of the emitter and an associated switching transition of the light output of the emitter. Similarly, there is a time delay between the on-off transition of the drive current of the emitter and the associated off-on transition of the light output of the emitter. This time dela...

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Problems solved by technology

[0004] [4] The time delay associated with laser or LED switching on or off is detrimental for higher speed applications, e.g. when the transmitter is modulated at frequencies in excess of about 10 to 100 MHz, depending on the design of the transmitter

[0010] [10] Among other disadvantages, many existing pulse shaping circuits cannot distinguish between the rising and falling edges of the driving electrical pulse; that is, the peaking pulse applied to the rising edge by the circuit is also applied to the falling edge of the driving pulse with the same amplitude

However, some types of optical transmitters, namely many types of semiconductor lasers, require a larger peaking pulse on the rising edge of the drive current pulse than on the falling edge of the drive current pulse, because lasers generally require more on-pulses than off-pulses. big open pulse

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