JPH0535613Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field of the Invention] The present invention relates to a current mirror circuit type gain control circuit using a current mirror circuit suitable for semiconductor integrated circuits.

[Technical background of the invention]

FIG. 3 shows a conventional current mirror circuit type gain control circuit, which consists of a current mirror circuit consisting of a diode-connected transistor (hereinafter referred to as a diode) D1 and a transistor Q1, an input signal source 9, and a variable resistor R. 2 is an output terminal. Variable resistor R connected to the cathode of diode D1
By varying the value of V, the voltage between its terminals V
changes, the base voltage of transistor Q1 changes, and the output current is varied.

In such a current mirror circuit, the signal current is I ₁ ,
The output current is _I2 , and the forward voltage of diode D1 is
Let V _BE1 be V BE1, and let V _BE2 be the voltage between the base and emitter of transistor Q1. The voltage between the terminals of resistor R is V
Then, I ₁ = I _s · A ₁ ... (1) I ₂ = I _s · A ₂ ... (2) V _BE2 = V _BE1 + V ... (3).

A is A ₁ = expV _BE1 /V _T , A ₂ = expV _BE2 /V _T
It is expressed as Incidentally, V _r indicates a thermal voltage, and I _s indicates a reverse saturation current. Further, the relationship between the signal current I ₁ and the output current I ₂ is expressed as I ₂ =I ₁ ·A (4) from equations (1), (2), and (3). However, A is expressed as A=expV _BE /V _T , and is considered to be approximately equal to the base-emitter voltage V _BE of transistors formed on the same semiconductor substrate.

Therefore, as shown in equation (4), the output current I ₂
is set to A times the input current _I1 . That is, by varying the variable resistor R and changing the voltage V between its terminals, the magnification of the current mirror type amplifier circuit can be arbitrarily set.

However, in the case of FIG. 3, since the variable resistor R is connected, a terminal for leading to the outside is required because it is externally connected, and as it is, it is not suitable for semiconductor integrated circuits. Furthermore, in order to improve the accuracy of the amplification factor of the current mirror circuit, it is necessary to improve the control of the current source supplied to the current mirror circuit.

In addition, it is difficult to obtain an amplifier circuit that operates a current amplification type gain control circuit with a constant voltage source of 1V or less, and in a current mirror circuit, there is a problem with inconsistency in diode characteristics due to the combination with transistors with different polarities. There is a problem that an offset occurs due to this.

[Purpose of invention]

The present invention was made to solve the problems of gain control circuits having current amplification circuits as described above, and its main purpose is to provide a current amplification circuit that operates at low voltage and is easy to amplify signals. A current mirror circuit type gain control circuit is provided.

Another object of the present invention is to provide a current mirror circuit type gain control circuit that has less offset caused by mismatching caused by combination with transistors of different polarities.

[Summary of the idea]

a current source of the first current mirror circuit is controlled by another current mirror circuit, and a bias of the first current mirror circuit at each connection point of the first current mirror circuit with the other current mirror circuit; The connection point on the side is used as an input terminal, the other connection point is used as an output terminal, and a predetermined current is supplied to a resistor connected to the emitter of the transistor on the bias side of the first current mirror circuit,
This is a current mirror type gain control circuit that operates at low voltage to obtain a current mirror type amplifier circuit with a predetermined amplification factor.

[Example of idea]

The current mirror circuit type gain control circuit of the present invention will be explained based on the embodiments shown in FIGS. 1 and 2.

In FIG. 1, 3 is a current mirror circuit consisting of a diode D1 and a transistor Q1, and current source transistors Q2 and Q3 of the current mirror circuit 3
forms a current mirror circuit 4 together with the diode D2. The cathode of diode D2 is grounded via current source 7. A connection point between the collector of transistor Q2 and an anode of diode D1 is connected to input terminal 1, and a common connection point between the collectors of transistors Q1 and Q3 is connected to output terminal 2. On the other hand, a current source 8 is connected to the connection point between the diode D1 and the resistor R1.

The operation of the gain control circuit of such a current mirror circuit will be explained. The current mirror circuit 3 is supplied with a mirror current I ₁ and a mirror current I ₀ limited by a resistor R1 via current source transistors Q2 and Q3. An input current source (±I _IN ) is input from the input terminal 1, is superimposed on the mirror current I ₁ , and a current of I ₁ ±I _IN is supplied to the diode D1. Further, a constant current I is supplied from a current source 8 to obtain a constant gain. An output current of ±I _IN ·A is output from the output terminal 2, as in the embodiment shown in FIG. A is
expV _BE /V _T , and the voltage V between the terminals of resistor R1 is
[(I _IN ±I _IN )+I]R1. Therefore, constant current I
By setting ? to a predetermined value, a current amplification type amplifier circuit having an arbitrary gain can be easily provided. Also, although not shown, resistor R2 and transistor Q2
The offset can be easily eliminated by drawing a constant current I from the connection point with the emitter.

Next, based on another embodiment of the present invention shown in FIG.
The current mirror circuit type gain control circuit of the present invention will be explained. In the embodiment of FIG. 1, the NPN transistor D1 is diode-connected to the PNP transistor Q2, and the PNP transistor Q3 is
Offsets occur due to mismatched diode characteristics of NPN transistor Q1. Especially 1V
In the following low voltage sources, this becomes noticeable and becomes a problem. Therefore, if accuracy of the output level is required, the offset can be eliminated by the embodiment shown in FIG.

The following description will be made based on the embodiment shown in FIG. Current source transistors Q2 and Q3 of current mirror circuit 3
In this case, the current source of the current mirror circuit 3 is controlled by the current mirror circuits 4 and 5, respectively. Diodes D2 and D on the bias side of the current mirror circuits 4 and 5
3 are transistors Q4 and Q5 of the current mirror circuit 6
connected to. The current mirror circuit 6 is composed of a diode D4 and transistors Q4 and Q5, and the emitter of the transistor Q4 is connected to the connection point between the resistor R1 and the diode D1. Therefore, the current mirror circuit 6 is formed of transistors with the same polarity as the current mirror circuit 3, and the mirror currents I ₁ and I ₀ having the same characteristics as the diode characteristics of the NPN transistor are applied to the diodes 2 and D3 in the current mirror circuit 3. It is possible to completely eliminate offsets caused by differences in diode characteristics of transistors with different polarities.

Further, an output current of ±I _IN ·A can be obtained from the output terminal 2. A predetermined gain is set by supplying a constant current from the current source 8 to the resistor R1 in order to adjust the gain to a predetermined value. Of course, the gain of the current amplification circuit can be easily controlled by supplying a variable current to the resistor R1.

As mentioned above, a current amplification type gain control circuit such as the embodiment shown in FIG. 2 is effective in a circuit where the occurrence of offset is to be avoided. Of course, the current amplification factor is set by the voltage drop across the terminals of resistor R1 caused by the current I supplied to resistor R1.

In addition, in the current mirror circuit type gain control circuit of the present invention, since it is operated by the saturation voltage V _{CE (sat)} of the transistor, V _BE of the transistor, and the voltage V of the resistor R1, the voltage V of the resistor R1 is approximately 0.9V. It is an effective amplifier circuit for low voltage sources.

[Effect of idea]

The current mirror circuit type gain control circuit of the present invention is
It can be used with a low voltage source of 1V or less, and the amplification factor can be easily and accurately set without using an external variable resistor. Of course, if the current value of the current source 8 is varied, it can be effectively used as a gain control circuit for a radio receiver or the like.

In addition, in such a current mirror circuit type gain control circuit, the offset voltage is particularly noticeable in a low voltage source, but in applications where offset voltage is a concern, it is necessary to use diodes with the same polarity as shown in the embodiment of Fig. 2. By constructing a current source created by a transistor with special characteristics, it is possible to obtain an output voltage with a small offset voltage.

[Brief explanation of the drawing]

1 and 2 are diagrams showing an embodiment of a current mirror type amplifier circuit according to the present invention, and FIG. 3 shows a conventional current mirror type amplifier circuit. 1...Input terminal, 2...Output terminal, 3 to 6...
...Current mirror circuit, 7...Current source, 8...Variable current source.

Claims (1)

[Claims for Utility Model Registration] (1) A first current mirror circuit consisting of a first diode and a first transistor includes second and third transistors for current sources of the first current mirror circuit. a second current mirror circuit connected to each other, the second and third transistors for the current source serve as output stages of the current mirror circuit, and the connection point between the first diode and the second transistor is input. a terminal, a connection point between the first transistor and the third transistor as an output terminal, and a connection point between the first transistor and the third transistor as an output terminal;
A resistor is connected to the cathode side of the diode,
A current mirror circuit type gain control circuit characterized in that a predetermined gain is obtained by connecting a current source to the connection point. (2) the second output stage of the second current mirror circuit;
and the third transistor form a current mirror circuit, a diode on the bias side of the current mirror circuit being connected to the first and second transistors of the output stage of the third current mirror circuit; 2. A current mirror circuit type gain control circuit according to claim 1, wherein the emitter of the second transistor is connected to the cathode of the first diode.