JP3392682B2 - Mixer circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mixer circuit required when modulating or demodulating an analog signal.

[0002]

2. Description of the Related Art Frequency conversion of signals is an indispensable technology in the fields of broadcasting and communication. FIG. 5 shows a double balance type mixer which has been generally used conventionally. This type of mixer works as follows. That is,
A signal input from the differential input terminal in1 is added to the bases of the emitter-coupled transistor pair Q1 and Q2, and appears as a current signal in the collectors of the transistor pair Q1 and Q2. It is the emitter current of Q4 and Q5, Q6.

On the other hand, the emitter-coupled transistor pair Q
A signal input from the differential input terminal in2 is applied to the bases of Q3, Q4, Q5, and Q6, so that the collectors of the emitter-coupled transistor pairs Q3, Q4, Q5, and Q6 are input from the differential input terminal in1. A current obtained by multiplying the signal by the signal input from the differential input terminal in2 appears, and the voltage is converted by the load resistors R1 and R2 and output.

However, in the conventional double-balance type mixer circuit, the voltage drop of the DC current source I1, the two stages of the base-emitter voltage of the transistor, and the voltage drop of the load resistance are applied in series, so that the amplitude of the signal is increased. There is a problem that a high power supply voltage is required in order to sufficiently secure the above and obtain a good distortion characteristic.

[0005]

As described above, the conventional mixer circuit requires a high power supply voltage, and in a circuit having a low power supply voltage, the distortion increases as the signal amplitude increases, and the distortion increases. There is a problem that if it is attempted to reduce the signal amplitude, the signal amplitude needs to be reduced accordingly.

An object of the present invention is to increase the amplitude of a signal that can be handled and obtain a sufficient distortion characteristic even at a low power supply voltage.

[0007]

In order to solve the above-mentioned problems, in the mixer circuit of the present invention, the first and second
A differential signal input terminal, a differential signal output terminal, and
Means for adding a positive phase signal of the differential signal input from the differential signal input terminal of the above and a positive phase signal of the differential signal input from the second differential signal input terminal to obtain a first added signal And adding a positive phase signal of the differential signal input from the first differential signal input terminal and a negative phase signal of the differential signal input from the second differential signal input terminal, Means for obtaining a summed signal, and a sum of the negative phase signal of the differential signal input from the first differential signal input terminal and the positive phase signal of the differential signal input from the second differential signal input terminal And a means for obtaining a third addition signal, a reverse-phase signal of the differential signal input from the first differential signal input terminal, and a differential signal input from the second differential signal input terminal. Means for adding a negative phase signal to obtain a fourth added signal, and a signal obtained by subtracting the second added signal from the first added signal A first differential amplifier circuit for amplifying a,
A second differential amplifier circuit that amplifies a signal obtained by subtracting the third added signal from the fourth added signal, and outputs of the first and second differential amplifier circuits are added, and the differential signal is added. And a circuit for taking out to an output terminal.

[0008]

By the above-mentioned means, the common-mode potential difference between the signal input points of the first and second differential amplifier circuits and the current merging point on the low potential side is changed by the first differential input signal, and the second differential input signal is changed. Since the differential input signal is input to the first and second differential amplifier circuits as a differential signal,
The circuit for changing the in-phase current of the differential amplifier circuit is not required to be connected in series with the first and second differential amplifier circuits in the power supply voltage direction, and it is possible to operate at a low power supply voltage.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a circuit diagram for explaining the first embodiment of the present invention. The positive phase input + of the differential input terminal in1 is connected to the collector of the transistor Q1 whose emitter is grounded via the resistor R1. Reverse phase input of differential input terminal in1 −
Is connected to the collector of a transistor Q2 whose emitter is grounded via a resistor R2. The base of the transistor Q1 is connected to the collector of the transistor Q1 via the resistor R3 and also to one of the resistors R5 and R6.
The other side of the resistor R5 is connected to the base of the transistor Q3, and the differential input terminal in2 is connected via the capacitor C1.
Connect to the positive phase input + of. The other end of the resistor R6 is connected to the base of the transistor Q4 and is also connected to the positive phase input + of the differential input terminal in2 via the capacitor C3. The base of the transistor Q2 is connected to the collector of the transistor Q2 via the resistor R4, and the resistors R7, R
8 to one side. The other side of the resistor R7 is a transistor Q
5 and the positive-phase input + of the differential input terminal in2 via the capacitor C2. Resistance R
The other of 8 is connected to the base of the transistor Q6, and is also connected to the positive phase input − of the differential input terminal in2 via the capacitor C4. Transistors Q3, Q4 and Q5, Q
Each 6 constitutes an emitter-coupled transistor pair.

The collector of the transistor Q3 is a resistor R9.
Through the resistor R12 to the power supply Vcc via the resistor R12. Transistor Q
The collectors of Q3 and Q4 are connected to the differential output terminal Out. The emitter of the transistor Q3 is grounded via the resistor R10, and the emitter of the transistor Q4 is grounded via the resistor R13. A resistor R11 is inserted and connected between the emitters of the transistors Q3 and Q4. Transistors Q5, Q6
Is connected to the differential output terminal Out, the emitter of the transistor Q5 is grounded via the resistor R14, and the emitter of the transistor Q6 is grounded via the resistor R16. A resistor R1 is placed between the emitters of the transistors Q5 and Q6.
Insert and connect 5.

The operation of the circuit thus constructed is as follows. That is, the positive phase input of the differential input terminal in1 +
The signal inputted from appears as an in-phase component in both collectors of the transistors Q3 and Q4 by the current mirror,
The emitter current of this emitter-coupled transistor pair is changed. Similarly, a signal input from the negative-phase input − of the differential input terminal in1 appears as a common-mode component in both collectors of the transistors Q5 and Q6 by the current mirror, and changes the emitter current of this emitter-coupled transistor pair.

As a result, the transistors are connected in the power supply direction by 2
Transistors Q3 and Q4 which are emitter-coupled pairs by the signal input from the differential input terminal in1 without being connected in series
This means that the emitter currents of Q5 and Q6 can be changed.

On the other hand, the signal input from the differential signal input terminal in2 appears as a differential component on the bases of the transistors Q3, Q4 and Q5, Q6 of the emitter coupled pair through the coupling capacitors C1 to C4. Transistor Q
The collectors and load resistors of 3, Q4 and Q5, Q6 have the same circuit as a conventional double balance mixer, which allows the system to operate as a mixer.

FIG. 2 is a circuit diagram for explaining the second embodiment of the present invention. In this embodiment,
For the positive phase input + of the input terminal in21, the collector is the power supply Vc.
At c, the emitter is connected to the base of a transistor Q21 whose ground is connected via a resistor R24. The positive-phase input − of the input terminal in21 is connected to the power supply Vcc at the collector and to the base of the transistor Q22 whose emitter is grounded via the resistor R29.

The positive phase input + of the differential input terminal in22 has a collector connected to the power supply Vcc via the resistor R1 and an emitter connected to the connection point between the emitter of the transistor Q21 and the resistor R24 via the resistor R22. It is connected to the base and also to the base of the transistor Q26. The positive-phase input − of the input terminal in22 has a collector connected to the power supply Vcc via the resistor R25 and an emitter connected to the resistor R25.
26 through the emitter of transistor Q21 and resistor R2
The transistor Q24 is connected to the base of the transistor Q25 and the base of the transistor Q25. The emitter of the transistor Q25 is connected to the connection point of the emitter of the transistor Q22 and the resistor R29 via the resistor R7, and the emitter of the transistor Q26 is connected to the resistor R30.
Is connected to the connection point between the emitter of the transistor Q22 and the resistor R29.

A resistor R23 is inserted and connected between the emitters of the transistors Q23 and Q24. Transistor Q25,
A resistor R28 is inserted and connected between the emitters of Q26. The collectors of the transistors Q23 and Q25 and the collectors of the transistors Q24 and Q26 are connected to the differential output terminal Out. The transistors Q21 and Q22 form a pair of emitter followers, and the transistors Q23 and Q24
And Q25 and Q26 are a pair of emitter-coupled.

The operation of this circuit is as follows. That is, the signal input from the input terminal of the differential input terminal in21 is impedance-converted through the transistors Q21 and Q22, appears as a voltage at the non-ground side terminals of the resistors R24 and R29, and the transistor pair Q23, Q23.
The common mode current flowing through 24, Q25 and Q26 is changed.
On the other hand, the signal input from the input terminal of the differential input terminal in22 is the transistor pair Q23, Q24 and Q2.
5, applied to the base of Q26 to change the differential current. Transistor pair Q23, Q24 and Q25, Q26
The collector and load resistance of the device form a circuit of the same type as a conventional double balance mixer, which allows the system to operate as a mixer.

If the output impedance of the signal source driving the differential input terminal in21 is low, the emitter follower transistor pair Q21, Q22 is unnecessary.

Also in this embodiment, since the current of the emitter-coupled transistor pair is controlled without connecting two transistors in series in the power supply voltage direction, operation at a low power supply voltage is possible. FIG. 7 is a circuit diagram for explaining a third embodiment of the present invention. This embodiment is an example in which a differential amplifier circuit is added to the differential input terminal portion of the mixer circuit of FIG. 1, and the same components as those in FIG. .

First, the part of the configuration different from that of FIG. 1 will be described. Positive phase input of differential signal input terminal in1 +
Are transistors Q31, Q32 and resistors R31, R
It is connected to the base of the transistor Q31 of the differential amplification emitter coupling circuit constituted by 32. Differential signal input terminal i
The positive phase input + of n1 is connected to the base of the transistor Q32 of the differential amplification emitter coupling circuit. Transistor Q3
The emitters of 1 and Q32 are grounded via the current source I31. The collector of the transistor Q31 is connected to the power supply Vcc via the resistor 31, and the collector of the transistor Q32 is connected to the power supply Vcc via the resistor 32. A transistor Q33 having a base connected to a connection point between the collector of the transistor Q31 and the resistor 31 has an emitter connected to the collector of the transistor Q1 and a collector connected to the power supply Vcc. The transistor Q34, whose base is connected to the connection point between the collector of the transistor Q32 and the resistor 32, has its emitter connected to the collector of the transistor Q2 and its collector connected to the power supply Vcc.

The operation of the system thus configured will be described. The signal input from the differential signal input terminal in1 is amplified by the transistors Q31 and Q32 and the resistors R31 and R32 that form the differential amplification emitter coupling circuit, and the amplified signal is further added to the transistor Q33.
It is converted into a current by the resistors R1 and Q34 and the resistor R2. The subsequent operation is the same as in the case of FIG.

In this embodiment, the transistors are connected in series in two stages in the power supply voltage direction, but the differential input terminal in
When the output of the local oscillator is put in 1 for modulation or demodulation, the distortion of this signal does not usually cause a problem, so that the voltage drop of the resistors R31 and R32 can be set low. Therefore, it can be used with a lower power supply voltage than the conventional double balance mixer.

FIG. 4 is a circuit diagram for explaining the fourth embodiment of the present invention. In this embodiment,
This is an example in which a circuit for injecting a direct current into the emitter of the emitter-coupled transistor pair of the circuit of FIG. 1 is added, and the same parts as those of the configuration of FIG.

In this embodiment, current sources I41 to I41 are connected between the power supply Vcc and the emitters of the transistors Q3 to Q6, respectively.
The component part to which I44 is connected is different from that in FIG. Although the current sources I41 to I44 are represented by symbols, since there is a potential difference of at least the base-emitter voltage of the transistors or more between the emitter potential of the emitter-coupled transistor pair and the power supply potential, it is possible to use a pnp-type transistor. , A current source can be easily realized.

In this embodiment, the transistors Q3 ...
By injecting a direct current into each emitter of Q6, the current flowing through the transistors of the emitter-coupled transistor pair is reduced and the mirror ratio of the current mirror is increased. As a result, the conversion gain of the mixer can be increased.

[0027]

As described above, according to the present invention,
Since the emitter current of the emitter-coupled transistor pair is changed by the differential signal input from the input terminal without connecting the emitter-coupled transistor pair in series in two stages in the power supply direction, a large amplitude and low distortion characteristics can be obtained even with a low power supply. Can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram for explaining a first embodiment of the present invention.

FIG. 2 is a circuit diagram for explaining a second embodiment of the present invention.

FIG. 3 is a circuit diagram for explaining a third embodiment of the present invention.

FIG. 4 is a circuit diagram for explaining a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram for explaining a conventional mixer circuit.

[Explanation of symbols]

Q1-Q6, Q21-Q26 ... Transistors, R1-R
16, R21 to R30 ... Resistance, in1, in2, in2
1, in22 ... Differential input terminal, Vcc ... Power supply, Out ...
Differential output terminal.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-8-222960 (JP, A) JP-A-62-194709 (JP, A) JP-A-9-260956 (JP, A) JP-A-9- 46138 (JP, A) International publication 96/41295 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03D 7/14

Claims (2)

(57) [Claims] 1. A first differential signal input terminal, a second differential signal input terminal, a differential signal output terminal, a positive phase signal of a differential signal input from the first differential signal input terminal, and the second differential signal input terminal. Means for adding a positive phase signal of the differential signal input from the differential signal input terminal to obtain a first addition signal; and a positive phase signal of the differential signal input from the first differential signal input terminal And a means for adding a negative phase signal of the differential signal input from the second differential signal input terminal to obtain a second added signal, and a differential input from the first differential signal input terminal. Means for adding a negative-phase signal of the signal and a positive-phase signal of the differential signal input from the second differential signal input terminal to obtain a third added signal, and from the first differential signal input terminal The opposite phase signal of the differential signal input and the opposite phase signal of the differential signal input from the second differential signal input terminal are added. Means for obtaining a fourth addition signal; a first differential amplifier circuit for amplifying a signal obtained by subtracting the second addition signal from the first addition signal; and a third differential signal from the fourth addition signal. A second differential amplifier circuit for amplifying a signal obtained by subtracting the addition signal, and a circuit for adding outputs of the first and second differential amplifier circuits and taking out to the differential output terminal are provided. Characteristic mixer circuit. 2. The mixer circuit according to claim 1, wherein a direct current is caused to flow through the emitter terminals of the first and second differential amplifier circuits to change the bias voltage at the emitter terminals, thereby performing conversion. A mixer circuit characterized by increased gain.