JPS5812460Y2 - Nonlinear distortion correction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nonlinear correction circuit that corrects nonlinear distortion of a light emitting diode.

The light output characteristic of a light emitting diode with respect to the drive current is relatively linear, but when a large drive current is applied to improve the S/N ratio, the drive current I The characteristic of the optical output P relative to the light emitting diode is a non-linear characteristic, and when a sinusoidal driving current shown by a is supplied to the light emitting diode, an optical output containing distortion as shown by b is obtained.

This type of distortion is called nonlinear distortion, and in order to reduce nonlinear distortion, it is sufficient to reduce the modulation degree, that is, the amplitude of the drive current, but this has the disadvantage of deteriorating the S/N ratio. .

An object of the present invention is to reduce nonlinear distortion by compensating for the nonlinear characteristics of a light emitting diode.

Examples will be described in detail below.

FIG. 2 shows the main circuit of an optical transmitter including a nonlinear distortion correction circuit according to an embodiment of the present invention. In the same figure, Tr, to Tr3 are transistors, LED is a light emitting diode, D is a diode, and R1 R4 is a resistor, R5 is a variable resistor, IN is an input terminal, E is a power supply terminal, and Pl is a correction power supply terminal.

1st stage NPN) transistor Tr1, 2nd stage PNP transistor Tr2, and 3rd stage NPN) transistor T
r3 amplifies the input signal from the input terminal IN, supplies a driving current corresponding to the input signal to the light emitting diode LED, and sends out the optical output of the light emitting diode LED through an optical fiber or the like.

At this time, the diode D is at the emitter potential of the transistor Tr2.

When the voltage difference between Tr2 and the corrected power supply voltage 2 is applied, and the level of the input signal increases, the emitter potential of the transistor Tr2 decreases, and since VE<VP, the transistor Tr2 is turned on.

When the diode D is on, the emitter current Ie of the transistor Tr2 is the sum of the current ir flowing through the resistor R3 and the current i flowing through the diode D, Ie = ir+
The driving current of the light emitting diode LED is I =
A(ir+id).

However, A is a proportionality constant.

As mentioned above, when the level of the input signal becomes high, the diode D is turned on to supply the current id, so by appropriately setting the corrected power supply voltage vP and the magnitude of the current flowing through the diode D, light emitting diode LE
It is possible to correct the non-linear distortion of D.

The following table compares the conventional case A and the case B where the nonlinear distortion correction circuit of the present invention is applied. In the table, APL is the average picture level (AVe).
ragePiClureLevel) and the LED modulation current are peak-to-peak (p-p) values.

As can be seen from the table, in the conventional case A, a bias current of 50 m is applied to the light emitting diode LED before applying the input signal.
A is flowing, and when an input signal is applied, the modulation current p-p
Since the value is 70 mA and it does not supply a current for correcting the nonlinear distortion of the light emitting diode LED, the driving current of the light emitting diode LED varies in the range of 15 to 85 mA with 50 mA as a reference, and therefore APL5
Differential gain at Q% is 9.0%, differential phase is 2.0°
This results in an optical output with large distortion.

However, when the nonlinear distortion correction circuit of the present invention is applied, B supplies a current for correcting the nonlinear distortion of the light emitting diode LED, so the driving current of the light emitting diode LED is 15 ~85+αmA (where α is the correction value), so APL 50
%, the differential gain is 1%, and the differential phase is relatively small, 1.5°, so an optical output with small distortion can be obtained.

As explained above, the present invention has a diode that is turned on when the input signal level is above a predetermined level, and is configured to supply current to correct the nonlinear distortion of the light emitting diode through the diode. Therefore, nonlinear distortion can be improved without deteriorating the S/N ratio.

[Brief explanation of drawings]

FIG. 1 is a characteristic curve diagram of light output characteristics versus drive current of a light emitting diode, and FIG. 2 is a circuit diagram including a nonlinear distortion correction circuit according to an embodiment of the present invention. Tr□ to Tr3 are transistors, LED is a light emitting diode, D is a diode, R□ to R4 are resistors, R5 is a variable resistor, IN is an input terminal, E is a power supply terminal, and P□ is a correction power supply terminal.

Claims (1)

[Scope of utility model registration request] In a circuit that supplies a driving current corresponding to an input signal to a light emitting diode, a diode that is turned on when the level of the input signal is higher than a predetermined level is provided, and nonlinear distortion of the light emitting diode is reduced through the diode. A nonlinear distortion correction circuit characterized by having a configuration that supplies current for correction.