JPH02159106A - Gain stabilizing amplifier - Google Patents

Abstract

PURPOSE:To stabilize the gain by connecting a variable current source to a node point where the current flowing to an amplifier stage transistor and setting the output current of the variable current source in order to offset the change of the bias current value of the amplifier stage transistor. CONSTITUTION:A variable current source IO is connected to the emitter of a transistor TRQ1 forming a normal TR amplifier, and the emitter voltage is kept at a constant level. In this case, the emitter potential V1 is compensated with connection of the current source IO. Thus the gain is never changed despite the variance of the power voltage VC.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gain stabilizing amplifier using transistors.

FIG. 1 is a circuit diagram showing a first embodiment to which the present invention is applied. In this embodiment, a variable current source IO is connected to the emitter of a transistor Q+ constituting a normal transistor amplifier, and its emitter voltage is held constant.

Here, the variable current source ■. is the second
It is assumed that the output characteristics shown in the figure are shown.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

Now, assuming that there is no current source I0, the gain A is determined by the current I flowing through the transistor q1, so it is given as follows. Here, e: elementary charge, k: Boltzmann constant, v1: base-emitter voltage.

In the above equation (1), suppose VC=5V, R,
=32kQ, R2=18kQ, VB! =0.8V
, Rc=1kQ.

When RC=1 and Ω, the gain varies greatly from 45 times to 31.5 times with respect to a variation of VC of ±0.5V. However, if current source I0 varies as shown in FIG. 2, the gain does not change with respect to variations in vc.

This is because the gain is determined by the current I flowing through the transistor q1, and the current source ■. This is because when there is no voltage, I is determined by the emitter potential v1 of the transistor Q+, and vl is subject to fluctuations in VC. Therefore, the gain A fluctuates, but when a current source of 1° is connected as in this embodiment, the gain A changes. Since this compensates for the emitter potential V, no change in gain occurs even with fluctuations in the power supply voltage VC.

In the embodiment shown in Fig. 1, the emitter potential determines the current I flowing through the transistor, so a current source I0 is connected to the emitter, but if it is determined by the collector side potential, then the current I flowing through the transistor is determined by the emitter potential. , current source to the collector■. ′ can be connected. This also applies to FETs.

Here, since the current source has extremely high output impedance, it does not adversely affect AC operation. Note that if the capacity of the current source adversely affects the characteristics of the amplifier circuit, a resistor may be inserted between the current source and the node that determines the bias current of the amplification transistor.

Also, such a current source ■. and I0' can be set to compensate the transistor gain not only for power supply voltage fluctuations but also for temperature changes, making it possible to create an amplifier with a constant gain over a wide range.

In particular, the circuit shown in FIG. 3 is suitable for a preamplifier for optical reception. That is, since the response band of the optical receiving preamplifier is proportional to the gain, if the band is insufficient, the signal cannot be transmitted, and if the band is excessive, noise increases and sensitivity deteriorates. Therefore, as shown in Fig. 3, a current source ■ is used. ' If there is no ', the gain will fluctuate greatly with the fluctuation of the power supply vc = +5V ±0.5■, and the band will be -31% to + + with respect to the set value.
It fluctuates greatly at 91%. However, the above current source ■
. By providing ', the band can be made constant.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, and FIG. 2 is a circuit diagram of the current source shown in FIG. 1. FIG. 3 is a circuit diagram showing the second embodiment of the present invention, and FIG. 4 is a diagram showing the output characteristics of the current source 10' shown in FIG. 1o, I. '...Current source, Ql...Transistor, vl...Emitter potential. [Effects of the Invention] As explained above, according to the present invention, the gain can be kept constant even with changes in the power supply voltage and external environment with the simple configuration of newly providing a current source, so it is possible to maintain the gain at a low cost. Applications to other fields (for example, optical receivers) are possible.

Claims (1)

[Claims] 1) In an amplifier using a transistor, a variable current source is connected to a node that determines the current flowing into the amplification stage transistor, and the output current of the variable current source is adjusted to offset changes in the bias current value of the amplification stage transistor. A gain stabilizing amplifier characterized by setting.