JPH0261168B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a constant modulation degree current modulation circuit, and more particularly to a constant modulation degree current modulation circuit that converts a voltage signal into a current signal weighted with a bias current in an integrated circuit. It is something.

[Technical background of the invention and its problems]

Conventionally, the current value was increased to 3 while keeping the current modulation degree constant.
A circuit shown in FIG. 5 is known as a constant current modulation circuit with a modulation degree that changes in stages.

That is, two transistors Q ₁ that operate differentially,
Loads RL ₁ and RL ₂ are connected to the respective collectors of Q ₂ , the base is used as an input terminal for input voltage signal V ₃ , and switches Sw ₁ and Sw ₂ are connected between the emitters.
Two resistors R ₁ and R ₂ that can be selected are connected in parallel, and each emitter outputs the same current value. It is designed to be connected to controlled constant current sources I ₁ and I ₂ .

Next, to explain the operation of this circuit, the input voltage signal Vs is transmitted between the emitters of transistors Q ₁ and Q ₂ , and the current i _RL1 flowing through the load RL ₁ of one transistor Q ₁ is the current of the constant current source I ₁ . Input voltage signal Vs to i ₁
is divided by the resistance between the emitters of transistors Q ₁ and Q ₂ .

That is, when the switch _Sw1 is closed, the modulation degree of _iRL1 is expressed by the formula (amplitude of Vs/ _R1 )/ _i1 .

In order to increase the level of current i _RL1 flowing through this load RL ₁ with a constant modulation factor, close switch Sw ₂ and change the connection of control terminal 2 to
The current _{i 1} of the constant current source I ₁ is changed so that the modulation degree of the current i _RL1 flowing through the load RL 1 _of Q ₁ becomes equal to the value of the formula.

To change the level one more step, press the switch.
It is necessary to close Sw ₁ and further change the connection of control terminal 2 to change _{i 1} so that the modulation degree of current i _RL1 becomes equal to equation (1).

However, when this circuit is integrated, the symmetry is broken because resistors R ₁ and R ₂ and switches Sw ₁ and Sw ₂ are connected between the emitters of the first and second transistors Q ₁ and Q ₂ . Therefore, there is a problem in that the low distortion amplification and high-speed operation characteristics that are characteristic of differential operation circuits cannot be fully demonstrated.

Furthermore, since the wiring for the switches Sw ₁ and Sw ₂ is extended and the terminals are provided outside the integrated circuit, there is a problem that the cause of unstable operation such as oscillation increases.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a constant modulation degree current modulation circuit that can change the current level with a constant modulation degree while maintaining differential operability. It is said that

[Summary of the invention]

That is, the present invention is basically a parallel connection circuit of two differential current modulation circuits, in which the bases of two transistors operating differentially are used as input terminals, a resistor is connected between the emitters, and the collectors of each transistor are connected in parallel. a first differential current modulation circuit, in which a load resistor is connected to the emitters, and a constant current source that applies the same current value to each emitter and can be simultaneously controlled to be activated or deactivated by a control circuit is connected to the first differential current modulation circuit; A second differential current amplification circuit configured similarly to the first differential current amplification circuit using two transistors and two constant current sources is connected in parallel to this first differential current modulation circuit. This is a constant modulation current amplification circuit.

[Embodiments of the invention]

Next, one embodiment of the present invention will be described with reference to FIG. However, the same reference numerals as in the conventional example indicate the same parts.

That is, the base is the input terminal, load resistors RL ₁ and RL ₂ are connected to the respective collectors, a first resistor R ₁ is connected between the emitters, and constant current sources I ₁ and I ₂ are connected to the respective emitters. The first connected
and a third transistor whose base and collector are commonly connected to the base and collector of the first transistor Q ₁ , respectively, to the first differential current modulation circuit composed of the second transistors Q ₁ and Q ₂ .
A second resistor R ₂ is connected between the emitter of Q 3 and the emitter of a fourth transistor Q ₄ whose base and collector are commonly connected to the base and collector of _the second transistor Q ₂ , respectively. Constant current sources I ₃ and I ₄ are connected to .

Among these, the constant current sources I ₁ , I ₂ , and I ₃ and I ₄ have the same current value, and each set of current sources is activated and deactivated at the same time by a control circuit 11 equipped with a control terminal 12. is controlled.

Furthermore, the modulation degree of the first differential current amplifier circuit composed of the first and second transistors Q ₁ and Q ₂ , the first resistor R ₁ , and the constant current sources I ₁ and I ₂ and the third and third transistors 4 transistors Q ₃ , Q ₄ and second resistor R ₂ constant current sources I ₃ , I ₄
The modulation degrees of the second differential current amplification circuits configured independently are set equal in advance.

Next, the operation of this embodiment will be explained.

That is, when the control circuit 11 selects the operation of only the constant current sources I ₁ and I ₂ , the load RL ₁ or
The degree of modulation for the current flowing through RL ₂ is expressed by the above equation, and the bias current is i ₁ .

Further, when the operation of only the constant current sources I ₃ and I ₄ is selected, the modulation degree is equal to the above formula and the bias current is i ₃ .

Furthermore, when the operation of both constant current sources I ₁ , I ₂ and I ₃ , I ₄ is selected, the modulation degree is equal to the above formula and the bias current is i ₁ +i ₃ .

That is, no matter which current source pair the control circuit 11 selects to operate, the modulation degree is constant only by changing the bias current, and it is possible to obtain a constant modulation degree current modulation circuit that maintains differential properties. I can do it.

Next, different modifications of the present invention will be explained with reference to FIGS. 2 to 4. However, the same reference numerals as those in the embodiment indicate the same parts, and no particular explanation will be given.

First, in the modification shown in Fig. 2, the constant current sources I ₁ and I ₂ are
are connected to the dividing points P ₁ and P ₂ of the resistor R ₁ , respectively,
The resistance value between the emitter of the first transistor Q ₁ and the dividing point P ₁ and the resistance value between the emitter of the second transistor Q ₂ and the dividing point P ₂ are made equal.

In the following modification of Fig. 3, the constant current sources I ₃ and I ₄ are connected to the second
is connected to the dividing points P ₃ and P ₄ of the resistor R ₂ , and the resistance value between the emitter of the third transistor Q ₃ and the dividing point P ₃ and the resistance value between the fourth transistor Q ₄ and the dividing point P ₄ are They are made equal.

The following modification shown in FIG. 4 is an example in which the NPN transistor in the circuit of the embodiment is replaced with a PNP transistor.

〔Effect of the invention〕

As described above, the present invention provides a constant modulation degree current modulation circuit that can change the bias current with a constant modulation degree while satisfying the characteristics of an integrated differential circuit, such as low distortion operation and high-speed operation. I can do it.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
3 and 4 are circuit diagrams showing different modifications of the present invention, and FIG. 5 is a circuit diagram showing a conventional example. 1, 11... Control circuit, 2, 12... Control terminal, I ₁ , I ₂ , I ₃ , I ₄ ... Constant current source, Q ₁ , Q ₂ , Q ₃ ,
Q ₄ ...transistor, R ₁ ...first resistor, R ₂ ...
...Second resistance, RL ₁ , RL ₂ ...Load.

Claims (1)

[Claims] 1 Loads RL ₁ and RL ₂ are connected to the respective collectors of two differentially operated transistors Q ₁ and Q ₂ , each base is an input terminal, and each emitter is connected to the same current. It is connected to the respective constant current sources I ₁ and I ₂ that output the value and is controlled simultaneously, and a first resistor is connected between both emitters.
a first differential current modulation circuit comprising R ₁ and an emitter of a third transistor Q ₃ whose base and collector are commonly connected to the base and collector of said first transistor, respectively; A fourth transistor commonly connected to the base and collector of the second transistor _Q2 , respectively.
The emitter of Q ₄ is connected to respective constant current sources I ₃ and I ₄ that have the same current value and are controlled simultaneously, and the third transistor Q ₃ and the fourth transistor Q are connected between both emitters. a second resistor having a value such that the degree of modulation of the collector current of No. ₄ is equal to the degree of modulation of the collector currents of the first transistor _Q1 and the second transistor _Q2 of the first differential current modulation circuit; A second differential current modulation circuit having R ₂ and a plurality of control terminals, the constant current sources I ₁ and I ₂ can be controlled by selecting whether to open or close these control terminals.
1. A constant modulation degree current modulation circuit comprising: a control circuit that controls operation/non-operation of the constant current sources I ₃ and I ₄ . 2. A constant current source I ₁ is connected to the dividing point P ₁ of the first resistor R ₁ , and a constant current source I ₂ is connected between the dividing point of the first resistor R ₁ and the emitter of the second transistor Q ₂ . The constant modulation current according to claim 1, wherein the constant modulation current is connected to a point where the resistance value of is equal to the resistance value between the emitter of the first transistor _Q1 and the dividing point _P1 . Modulation circuit. 3. A constant current source _I3 is connected to the dividing point _P3 of the second resistor _R2 , and a constant current source _I4 is connected between the dividing point of the second resistor _R2 and the emitter of the fourth transistor _Q4 . The modulation factor according to claim 1, characterized in that the modulation factor is connected to a point _P4 whose resistance value is equal to the resistance value between the emitter of the third transistor _Q3 and the dividing point _P3 . Constant current modulation circuit.