JPH0547124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current mirror circuit, and particularly to a current mirror circuit suitable for calculating high frequency signals.

[Conventional technology]

A current mirror circuit is used to configure a current calculation circuit. For example, as the simplest calculation, a constant coefficient circuit is constructed by a current mirror circuit in which the emitter area ratio is adjusted to a desired count. This type of current mirror circuit is described in Bipolar and Mos.
Analog Integrated Circuit Design, 1984, John Willy, Chapter 4 (Graben, "Bipolar and Mos Analog Integrated Circuits")
(ABGraben, Bipolar and MOS Analog
Integrated Circuits Design, 1984, John
Discussed in Wiley & Sons.Cpt.4).

[Problem that the invention seeks to solve]

The input side of the current mirror circuit is usually composed of one or more forward diode circuits. FIG. 2 shows an example of a doubling circuit using a current mirror circuit. The input terminal 111 of this circuit is lower than the reference (ground) voltage when V _BE is based on the base-emitter voltage of the transistors 151 and 152.
Only 2V _BE is at a higher voltage. Therefore, the input voltage
When V ₁ , assuming that each transistor is the same, the total emitter area of transistors 153 and 154 is twice that of transistor 151, so the output current I ₀ is I ₀ = 2I ₁ = 2 (V _{1 -} 2V _BE )/R ₁ and depends on the voltage V _BE . For this reason, the voltage
When V _BE changes due to temperature, etc., the output current I ₀ also changes, and when used with a low signal source voltage V ₁ (especially in the high frequency range, the voltage handled is low), the change in the output current I ₀ also becomes large. It was hot.

SUMMARY OF THE INVENTION An object of the present invention is to provide a current mirror circuit that can perform accurate calculations on input signals even at low voltages, especially at high frequencies, even when transistor characteristics vary.

[Means for solving problems]

The purpose of the above is to insert a control circuit composed of a variable impedance circuit or a variable voltage circuit between the common terminal connecting the emitters of the input and output transistors and the ground, and when a voltage change at the input point occurs, the This is achieved by providing a negative feedback loop that cancels out changes in the input terminal voltage by means of a control circuit.

[Effect]

When the input terminal voltage changes due to temperature fluctuations,
The negative feedback circuit changes the input terminal voltage of the control circuit, thereby keeping the input terminal voltage of the current mirror circuit constant. As a result, there is no fluctuation in the output current even when the input voltage is low, making it possible to perform highly accurate calculations.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In the figure, a current mirror calculation circuit 10
Signal voltages V ₁ to V ₅ are applied to input terminals 111 to 115 of 0 through resistors R ₁ to R ₅ . Input terminal 11 of common terminal 105 of current mirror circuit 100
A negative feedback control circuit 200 is inserted between the circuit and the circuit 5. The negative feedback control circuit 200 includes a transistor 220 as a variable impedance element and a differential amplifier 210. A reference voltage (not shown) as a target voltage of the input terminal 115 is applied to the reference input terminal 211 of the differential amplifier 210. The magnitude of this voltage is slightly higher than the voltage of the forward diode of the input terminal 115 of the current mirror arithmetic circuit 100, and is about the same value as V _BE in the conventional case shown in FIG.

In the above configuration, the negative feedback circuit 200
adjusts the current of transistor 220 so that the voltage at current mirror arithmetic circuit input terminal 115 is equal to the voltage at reference input 211 of amplifier 210. As a result, not only the input terminal 115 but also each input terminal voltage 11 having a configuration in which the forward voltage is approximately equal
1 to 114 are also controlled to have the same reference value. Therefore, the input terminal 115 has
Calculation input voltage V ₁ of other calculation inputs 111 to 114
If you apply a voltage _V5 that is about the average value of ~ _V4 ,
The arithmetic circuit 100 and the output current I ₀ are determined by the inputs V ₁ to V ₄ without depending on temperature fluctuations or the like.

The output is given by I ₀ = f (V ₁ , V ₂ , V ₃ , V ₄ ).

Here, various circuits can be considered as the current mirror arithmetic circuit 100, and it may be the double circuit described in FIG. 2. Another example is addition,
There are also subtractions, etc., and I will list them here.

FIG. 3 shows an adder circuit in which two current mirrors are connected in parallel. Current I ₁ from input terminal 111 and current I ₂ from input terminal 112 are added at output terminal 130 as follows.

I ₀ = I ₁ + I ₂ Figure 4 shows the same adder circuit with input terminals 111, 1
12 are provided in parallel to one current mirror circuit. The calculation formula is the same as that in FIG.

FIG. 5 shows an example of a subtraction circuit. The output I ₀ becomes I ₀ = I ₁ + I ₂ .

FIG. 6 also shows a subtraction circuit. The calculation formula is the same as that in Figure 5, but the circuit in Figure 6 is
Consists of only NPN transistors,
It is possible to operate at higher speed than the circuit shown in FIG.

FIG. 7 shows an embodiment of the multiplication/division circuit. This circuit consists of three current mirror pairs constituting an input stage and a differential pair of transistor output stages with fixed base voltages. Each input terminal 11
The input current flowing into 1, 112, 113 is I ₁ ,
When I ₂ and I ₃ and the output currents of the output terminals 130a and 130b are I ₀₁ and I ₀₂ , the following function holds true for each current.

I ₀₁ / I ₀₂ = I ₁ / I ₂ I ₀₁ + I ₀₂ = I ₁ Therefore, the output current I ₀₁ , I ₀₂ is I ₀₁ = I ₂ / (I ₂ + I ₃ )・I ₁ I ₀₂ = I ₃ / (I ₂ + I ₃ )・I ₁ . Although this arithmetic expression shows limited multiplication and division, this form is effective when applied to the brightness signal adjustment circuit of a CRT display device.

If such an arithmetic circuit as described above is used as the current mirror arithmetic circuit 100 shown in FIG. 1, the voltage of each input terminal is controlled to be constant, so highly accurate arithmetic is possible, and the current mirror circuit has good characteristics at high frequencies. By taking advantage of this, for example, low voltage operation of 5V or less at 100MHz becomes possible.

Next, another embodiment of the present invention will be described. FIG. 8 shows one embodiment, and the same or equivalent parts as in FIG. 1 are indicated by the same reference numerals. The circuit in Figure 8 is
This is a simple doubling factor for a current mirror operation circuit, and the output stage transistors 155 and 156 have an emitter area twice that of the input stage transistor 151. Transistors 153, 154
The circuit including the resistor 175 constitutes an input terminal voltage detection circuit for obtaining a terminal voltage almost equal to the input stage terminal voltage against temperature fluctuations, etc., and is made of the same type as the input side transistors 151, 155, etc. It consists of transistors of the same size. Therefore, the voltage at terminal 115 is almost equal to the voltage at terminal 111, including temperature changes.

The voltage at terminal 115 is applied to one input of differential amplifier 210, and the other input is connected to resistor 176,
A reference voltage _VB is provided by the voltage division of 177. The output of the amplifier 210 is connected to the base electrode of a transistor 220 as a variable impedance element inserted between the common terminal 105 of the arithmetic circuit and ground. Therefore, due to the above negative feedback control loop, the voltage at terminal 115 (≒terminal 11
1 voltage) will be equal to V _B. Output I ₀ in that case
I ₀ =2(V ₁ −V _B )/R, and since V _B does not fluctuate, it becomes a stable double coefficient circuit.

FIG. 9 shows another embodiment of the present invention,
This shows the main parts of a phase-locked circuit. That is,
Phase discrimination circuit 300 and its output switch 321,
322, a filter consisting of a resistor 351 and a capacitor 350, a current controlled oscillator (emitter-coupled multivibrator) 160 and its constant current control circuit transistors 151 to 153, and a bias constant current source 1
68, a control circuit 200 for a current addition point, and the like. One purpose of control in this circuit is to always keep the voltage at the current inflow point 111 at the switch 32.
The objective is to improve the control stability of the oscillator by controlling the voltage to be equal to the voltage at the voltage dividing point of 1,322. Therefore, the reference voltage to be controlled at the addition point 111 is the output switch 321 of the phase discrimination circuit 300,
Voltage divider circuit transistor 22 having the same configuration as 322
It is given by 1,222. By doing so,
Since the voltage when the output pulses of the phase discrimination circuit 300 overlap can be made equal to the reference voltage, the overlap does not become an offset on the oscillator side.

The reference voltage of the addition point 111 is V _CC /2
It is a comparison voltage of V _CC at or close to it.
Therefore, in that case, a CMOS inverter amplifier can also be used for the amplifier 210 and its bias circuit.

Although the present invention has been explained in detail using examples above, the present invention is not limited to the examples, and can be applied to various circuits using a current mirror circuit, a MOS circuit, a composite circuit of MOS and bipolar, etc. It is obvious that it applies to formats.

〔Effect of the invention〕

According to the present invention, since the current mirror circuit can be operated with high precision using a low voltage signal source, it is possible to realize an arithmetic circuit with high precision that operates at a high frequency.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a circuit showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of a conventional circuit, FIGS. 3 to 7 are partial circuit diagrams showing an application of the present invention, and FIGS. FIG. 9 is a circuit diagram showing other embodiments of the present invention. 100...Arithmetic circuit, 105...Common terminal, 1
11-115...Input terminal, 210...Differential amplifier, 220...Transistor.

Claims (1)

[Claims] 1. In a current mirror circuit in which the emitters of transistors are connected to a common potential, and which includes an output terminal and at least one input terminal, the voltage of one input terminal is compared with a reference voltage, and both 1. A current mirror circuit comprising voltage control means for controlling the common potential so that the common potentials are equal to each other.