JPS5899008A - Oscillation and modulation circuit - Google Patents

Abstract

PURPOSE:To obtain an oscillation and modulation circuit having flat frequency characteristics in modulation sensitivity, by connecting an element of a minute capacitance between input terminals of a varactor element and an active element as a part of an oscillation element connected to a modulation signal source and a bias source. CONSTITUTION:A circuit taking a transistor (TR)3, and a crystal oscillator 4 as major elements is oscillated in a radio frequency. A modulation signal is applied from an input terminal 1 via a coupling capacitor (C)5. A bias voltage is applied to a varactor diode 2 via a bias resistor (R)18 from a bias power supply terminal 17. A C16 having a minute capacitance is connected between a connecting point A with the C5, the R18 and the diode 2 and an input terminal 20 of the TR3. In this case, the C16 and the input resistor of the TR3 form a pass region for radio frequencies and a block region for the modulation frequency. Thus, a crystal oscillation modulation circuit having a flat frequency characteristic in the modulation sensitivity is obtained and used for high speed data transmission also.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oscillation modulation circuit that uses a crystal oscillator also as a modulator.

A conventional frequency modulation circuit is shown in FIG. The figure shows a modulated signal in the audio frequency band of 0.3 to 3 KHz with a radio frequency of 10
In the modulation circuit added to the oscillator for stones to several dozen, 1 is the input terminal of the modulation signal, 2 is the voltage variable capacitance element, 3 is the transistor,
4 is a crystal oscillator.

5 is a coupling capacitor for modulation signals, 6.7 is a capacitor that determines oscillation conditions, 8 is a capacitance compensation coil connected in parallel to crystal oscillator 4, 9 is an emitter resistor of transistor 3, 1o and 11 are paces, respectively. A resistor forming a bias voltage circuit, 12 a bypass capacitor connected to a power supply terminal 13, 14 a coupling capacitor, and 16 an output terminal where an oscillation output is generated.

In the above configuration, transistor 3. A circuit whose main element is a crystal oscillator 4 oscillates at a radio frequency.

A modulation signal applied from the modulation input terminal 1 is applied to the variable capacitance element 2, and its capacitance changes according to the modulation signal.
Frequency modulated.

However, since the signal applied from the modulation input terminal 1 is applied not only to the variable capacitance element 2 but also to the base of the transistor 3, the base bias changes with the modulation signal. Therefore, as shown in FIG. 21, the amplitude of the radio frequency output B was modulated by the modulation signal as shown by the envelope A.

Further, as shown in FIG. 3, when the modulation frequency becomes high, there is a drawback that the modulation sensitivity decreases as shown in C. In the figure, D and E are the effects of sub-resonance of the crystal resonator 4, which usually occurs at several tens of kHz.

The present invention aims to eliminate the above drawbacks and provide a crystal oscillation modulation circuit in which the frequency characteristics of modulation sensitivity are flat.

The present invention will be explained below along with examples thereof.

Fig. 4 shows an embodiment, and the circuit shown in Fig. 1 is different from that in which a capacitor 16 of minute capacity is provided between the transistor 3 and the coupling capacitor 5, and a bias voltage terminal (second bias source)
The only difference is that the bias applied from 17 is applied from resistor 18, and the rest is the same.

Next, the operation of the above embodiment will be explained. A DC bias voltage is supplied from the bias voltage terminal 17 to the variable capacitance element 2, and a modulation signal from the modulation input terminal 1 is superimposed thereon. At this time, when looking at the active terminal side from the connection point A, as shown in FIG.
A path circuit is formed. Therefore, by selecting the capacitance value of the capacitor 16 to be small, the above-mentioned path circuit can be set in the pass-through region at radio wave numbers, while being in the blocking region at the modulation frequency band. Therefore, since the active element side appears to be in an open state in the modulation signal, almost no modulation voltage is induced at the input terminal 20 of the active element 3, and therefore, its operation is not disturbed.

FIG. 7 shows the output waveform during the modulation operation of this embodiment, showing that no amplitude modulation occurs due to the modulation signal.

Further, FIG. 8 shows the modulation characteristics and shows that the frequency characteristics of modulation sensitivity are almost flat.

FIG. 6 shows another embodiment of the present invention, in which resistors 1o, 1
1. This circuit is used when the input resistance 19 of the active element is large. 21 is a high frequency coil that has a high impedance with respect to the oscillation frequency and acts at several milliohms with respect to the modulation frequency; and 22/"a large capacitance capacitor that bypasses the i modulation frequency." Other circuit elements correspond to those shown in FIG.

The modulation signal is divided by a microcapacitance capacitor 16 and a large capacitance capacitor 22, and almost no components that change the operating conditions of the active element 3 are generated, so that the same operation as shown in FIG. 4 is performed. .

Note that in the above embodiment, a polar transistor 3 is used as the main element for oscillation;
It is also possible to use active elements such as ET.

As explained above, according to the present invention, while preventing the modulation frequency from being applied to the input terminal of the active element,
By forming a no-innocent circuit that passes uncontrolled frequencies,
By ensuring that the modulation signal is applied only to the modulation element, the modulation sensitivity can be kept constant over a wide frequency range, so it can also be used in high-speed data transmission circuits, and its industrial value is outstanding. .

[Brief explanation of drawings]

Fig. 1 shows the results of a conventional oscillation modulation circuit, Fig. 2 shows the signal waveforms of its main parts, Fig. 3 shows its characteristics 1, and Fig. 4 shows the oscillation modulation circuit according to an embodiment of the present invention. A wiring diagram, Fig. 6 is an equivalent circuit diagram of the main part, Fig. 6 is a wiring diagram of another embodiment,
FIG. 7 is a signal waveform diagram of other important parts of the above H implementation, and FIG. 8 is a diagram of its characteristics. 2...Variable capacitance element, 3...Active element, 1
3...Power supply terminal, 16...Fine capacitance, 17...Bias voltage terminal, 2Q...Input terminal. Name of agent: Patent attorney Toshio Nakao /1-1)・
1 person Figure 1 Figure 2 Figure 3 Henken Shuoi E Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] an active element biased by a first bias source; a variable capacitance element connected to a modulation signal source and serving as a part of an oscillation element; , comprising a minute capacitor connected between the input terminal 2o of the active element and the variable capacitance element, and at least the minute capacitor and the input resistance of the active element block the modulation frequency and allow the oscillation frequency to pass. An oscillation modulation circuit characterized by forming a bypass circuit.