JPH06244642A - Modulator - Google Patents

Abstract

PURPOSE:To obtain a modulator low in the leakage of carrier wave with simple structure by connecting a diode to the collector of a transistor giving an output and performing the output through the diode. CONSTITUTION:A diode 9 is interposed between the collector of a transistor 8 and a resistor 4, and the output is extracted from the junction of the diode 9 and the resistor 4. In this case, the diode 9 may be connected to one or plural diodes in series, but is connected so that the polarity is reverse to the base collector diode of the transistor 8. Therefore, since the diode connection connected is reverse series to the path the base of the transistor 8 to the output is interposed, the impedance of this path is enhanced to reduce the leakage to the output of carrier wave. Thus, the noise ratio to an output signal is improved and this modulator is profitable for practical use.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to improvements in modulators using differentially coupled transistors.

[0002]

2. Prior Art and Problems: Prior art power supplies V _C , V of FIG.
A modulator with differentially coupled NPN transistors 2 and 3, properly biased at _E , operates as follows. A pair of carrier waves V ₇ and V ₈ having mutually opposite phases, which are typically rectangular waves, are applied to the bases of the transistors 2 and 3 by the carrier generation sources 7 and 8, and the transistors 2 and 3 are alternately turned on. And the low conduction state is repeated. Modulation input current I ₁ from the modulation signal source 1, since is diverted its substantial part to the transistor of the high conductive state, the resistor 4 which is connected to the collector of the transistor 3 is modulated carrier wave input current Is output. When only the AC portion of the output voltage is desired, the voltage output V is output to the load 6 via the decoupling capacitor 5.
_Take out ₆ .

In the circuit of FIG. 1, particularly when the input current is low, the carrier wave leaks through the collector-base impedance of the transistor 3 and is superimposed on the voltage output which is the modulated carrier wave, so that the input current is particularly low. At this time, the signal-to-noise ratio of the voltage output is reduced. The situation is shown in FIG.

In the figure, the input current I ₁ , the carrier voltage V ₈ and the voltage output V ₀ are shown with their time axes corresponding to each other. After time t, the leak component of V ₈ appears in V ₆ even though I ₁ is almost 0, and it becomes a noise output, and the signal-to-noise ratio deteriorates. There is also a method of canceling the leakage by introducing a signal equivalent to this leakage so as to have a reverse polarity, but the structure for that is complicated.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above problems by a modulator having a simple structure and a small carrier leakage.

[0006]

SUMMARY OF THE INVENTION In one embodiment of the present invention, a diode is connected to the collector of a transistor that provides an output, and the output is performed via the diode. Since the direction of the diode is reversed from the direction of the base-collector junction of the transistor, the impedance from the base of the transistor to the output side terminal of the diode is kept high,
Carrier leakage is reduced. On the other hand, there is virtually no effect of the diode on the modulated current, which improves the signal-to-noise ratio of the voltage output.

[0007]

FIG. 3 is a schematic circuit diagram of a modulator according to an embodiment of the present invention. Elements having the same function as in FIG. 1 are given the same reference numbers. The difference from the prior art of FIG. 1 is that a diode 9 is inserted between the collector of the transistor 8 and the resistor 4. Output is diode 9
And the resistor 4 are taken out from the connection point.

The diode 9 may be one or a plurality of diodes connected in series, but is connected so as to have a polarity opposite to that of the base-collector diode of the transistor 8. Therefore, because the base-to-output path of transistor 8 is intervened by an anti-series connected diode junction, the impedance of this path is increased, thus reducing carrier leakage to the output.

FIG. 4 is a schematic circuit diagram of another embodiment of the present invention. Elements having the same functions as in the embodiment of FIG. 3 are given the same reference numbers. In the embodiment of FIG. 4, in order to take out the output of the transistor 7, a series circuit of a resistor 10 and a diode 11 is inserted between the collector of the transistor 7 and the power source, corresponding to the resistor 4 and the diode 9. From the anode of each diode 9, 11 to the decoupling capacitor 5,
An output is taken out via 12, and an operational amplifier 14 and a resistor 6 are provided.
It is input to the amplifier composed of the resistor 13 and the resistor 13 and is output as a signal output. The resistor 13 is interposed between the non-inverting input terminal and the output terminal of the operational amplifier 14, and the resistor 6 is the operational amplifier 14.
Is inserted between the non-inverting input terminal and the ground. Resistance 4, 10
Have the same resistance value, and the resistors 6 and 13 have the same resistance value.

Even in the prior art (immediately, even if the diodes 9 and 11 are removed by short-circuiting in the circuit of FIG. 4), the effect of reducing the leakage of the carrier wave is obtained by the canceling effect, but in the circuit of FIG. Large attenuation.

FIG. 5 shows still another embodiment. Elements having the same function as in the circuit of FIG. 3 are given the same reference numbers. In this embodiment, the diode 9 is formed by connecting two Schottky diodes in series. An amplifier 52 and a resistor 54 are provided to provide the modulation input current I ₁ . The input signal is a voltage from DC to 10 kHz applied to the non-inverting input terminal 51 of the operational amplifier 52, which is a commercially available operational amplifier OP-07, as the voltage V ₁ .

When the circuit operation for the modulation signal is given, the inductances 53 and 55 (10 μH each) can be considered by removing the short circuit. The modulation input current I ₁ is applied to the resistor 54
The current flowing in (100Ω), the amplifier 52, the resistor 5
9, inductance 55, transistor 2, amplifier 52
The feedback path through the, is restricted to V _1/100. The resistor 59 (215Ω) and the diode 60 protect the base / emitter reverse bias of the transistor 2.

On the other hand, the carrier generation sources 7 and 8 are ECL circuits, and apply rectangular wave voltage outputs of 20 MHz to the bases of the transistors 2 and 3 (both are 2SC3357) in opposite phases via the coupling capacitors 57 and 58. . The resistance between the bases is about 50Ω, and the magnitude of the carrier voltage between the bases is about 0.4V peak-peak. When considering the circuit operation related to the carrier wave, the inductances 53, 55
May be removed openly.

The output taken out through the resistor 4 (56.2Ω) and the decoupling capacitor 5 (0.1 μF) is filtered by the low-pass filter 65 and the resistor 6 (5
0Ω). If the diode 9 is short-circuited and removed, the level of the leaked carrier wave will increase about 10 times

[0015]

By implementing the present invention, the leakage of the carrier wave to the output of the modulator is suppressed by a simple structure, so that the signal-to-noise ratio of the output signal is improved, which is useful for practical use. It should be noted that the elements of the illustrated circuit are not limited to the type and others and can take a wider range of element values, and if necessary, modifications on the circuit are allowed without losing the gist of the present invention. To be done.

[Brief description of drawings]

FIG. 1 is a circuit diagram of one embodiment of a prior art modulator.

FIG. 2 is a waveform diagram showing signal waveforms of various parts of the circuit of FIG.

FIG. 3 is a schematic circuit diagram of an embodiment of the present invention.

FIG. 4 is a schematic circuit diagram of another embodiment of the present invention.

FIG. 5 is a schematic circuit diagram of still another embodiment of the present invention.

[Explanation of symbols]

 1: Modulation signal source 7, 8: Carrier wave generation source

Claims (1)

[Claims] 1. Modulation for obtaining an output signal through a diode from at least one collector of a differential coupling transistor pair in which modulated signals are input to mutually connected emitters and carrier waves having mutually opposite phases are applied to respective bases. vessel.