JPH0411052B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a circuit configured to switch between two types of signals and drive an FM modulator with the switching signal, and particularly relates to a circuit configured to switch between two types of signals and drive an FM modulator with the switching signal. (below
This is very effective when using a VCO (abbreviated as VCO) as both an FM modulator and a PLL-type FM demodulator.

Conventional configuration and its problems When performing conventional FM modulation, the input voltage signal is
A common method was to obtain an FM modulated signal by inputting it to a VCO.

When performing FM demodulation, for example, when using the PLL method, a method is used in which the input FM modulation signal and the VCO output signal are phase-compared, and the error signal is input to the VCO through a low-pass filter and obtained as the output demodulated signal. was commonly used.

When performing FM demodulation using the PLL method in this way, FM modulation can also be performed by switching the input signal of the VCO used in the PLL circuit, and by switching the input signal of one VCO. Therefore, the FM modulator and FM demodulator can be integrated into one VCO.
It was possible to configure

FIG. 1 shows an example of a circuit configured to perform FM modulation and demodulation using one VCO.

When using this circuit as an FM modulator, switch 4 is switched to the M side and a modulation signal is input from input terminal 1. Modulation signal is DC at capacitor 2
After the components are removed, a reference bias voltage is applied through the variable resistor 3. This reference bias voltage determines the center frequency when FM modulated. The modulation signal to which the reference bias voltage has been added is input to the VCO 5 through the switch.
Since VCO5 is a circuit that oscillates a signal with a frequency proportional to the input signal voltage, this output signal is
It becomes an FM modulated signal and is output to the output terminal 6.

On the other hand, when using this circuit as an FM demodulator, switch switch 4 to the D side and input terminal 7.
Input the FM modulation signal. This FM modulated signal is input to a phase comparator 9 after the AM component is removed by a limiter circuit 8 . Phase comparator 9
is the FM modulation signal with AM component removed and VCO5
compares the phases of the output signals of and outputs the error voltage. The error voltage is outputted to the demodulation output terminal 11 through the low-pass filter 10, and is also inputted to the VCO 5 through the switch 4. These systems constitute a PLL loop, and work so that the output signal of the VCO 5 matches the input FM modulation signal in phase, that is, the frequency matches at all times. Then, the signal input to VCO5,
In other words, since the error signal of the phase comparator 9 is equivalent to the modulation signal that created the input FM modulation signal,
In other words, it can become an FM demodulated signal.

By switching the input signal of one VCO in this way, the FM modulator and FM demodulator can be combined into one
It is possible to configure with VCO, but here
Let's take a look at the switch (4 in Figure 1) that changes the input signal of the VCO. In addition to the basic performance of this switch, such as sufficient dynamic range and no crosstalk when switching signals,
No DC fluctuation when switching signals, input signal DC
Extremely high performance is required, including the ability to reliably transmit components. Therefore, in the past, it was extremely difficult to convert this switch into an electronic switch, and generally the only option was to use a mechanical switch or a relay.

Problems like this can be solved by converting this circuit configuration into an IC.
This has been a huge obstacle when trying to transform the system.

Purpose of the Invention The present invention improves the above-mentioned problems, and makes it possible to simultaneously configure an FM modulator and an FM demodulator with one VCO without using such a high-performance switch. All circuits are ICs
This provides a circuit configuration that can be converted into

Structure of the Invention The present invention includes a first means for converting a first voltage signal into a first current signal by a first voltage-current converter; second means for converting into a second current signal by a converter; a first current signal obtained by said first means; and a second current signal obtained by said second means. a fourth means for driving a current controlled oscillator with the added current signal obtained by the third means; and a first voltage-current converter. The voltage controlled oscillator with an input switch is characterized by comprising at least five means and a fifth means for controlling one of the second voltage-current converters to operate.

DESCRIPTION OF EMBODIMENTS FIG. 4 shows an example of a specific configuration of the present invention.
31 in the figure is a voltage controlled oscillator. This is an oscillator that oscillates a signal with a frequency proportional to the amount of current input and output of the input signal. Also 28 and 29
is a voltage-current converter that exchanges voltage information of an input signal into current information, that is, limits the amount of output current in and out according to the voltage of the input signal.

The modulation signal that enters input terminal 1 is transferred to capacitor 2.
After the DC component is removed, the signal is converted into a current signal by a voltage-current converter 28.

On the other hand, in the circuit forming the PLL system, the error voltage signal output from the phase comparator 9 also passes through the low-pass filter 10 and is then converted into a current signal by the voltage-current converter 29.

The modulation signal converted into a current signal and the error voltage signal converted into a current signal are added as they are and input into the current controlled oscillator 31. Here, the voltage-current converter 28 and the voltage-current converter 29 do not operate at the same time, but only one of them operates. In other words, when this circuit acts as an FM modulator, the switch 30 is switched to the M side, and the power output input from the power supply terminal 32 is applied to the voltage-current converter 28 on the modulation signal side. Only the voltage-to-current converter 28 is operated. Conversely, when the circuit is used as an FM demodulator, the switch 30 is switched to the D side, the power input from the power supply terminal 32 is applied to the voltage-current converter 29 on the error voltage side, and the voltage on the error voltage side is - Operate only the current converter.
Therefore, the current signal input to the voltage controlled oscillator 31 is either a modulation signal or an error signal, and the voltage-current converter converts the two input signals into the current signal state. It will be switched.

As described above, if the two signals are switched in the current signal state, sufficient dynamic range can be obtained even when the power supply voltage is low, and crosstalk and fluctuations in DC leakage current when switching signals almost never occur. do not.

In the configuration shown in FIG. 4, the operating side is switched by switching the power input applied to the two voltage-current converters 28, 29, but the reference of the two voltage-current converters 28, 29 is The two voltage-to-current converters 28, 29 can be connected by switching the bias current sources so that only one is operative.
The operating side may be switched. Further, the switch 30 can also be an electronic switch.

In FIG. 4, reference numeral 3 denotes a variable resistor 3 for bias current adjustment to determine the oscillation center frequency of the current controlled oscillator. Further, the limiter 8, phase comparator 9, and low-pass filter 10 perform the same operations as those in the circuit shown in FIG.

FIG. 2 shows a specific example of a conventionally commonly used VCO circuit. The circuit shown in the figure is an emitter-coupled multivibrator type. This circuit will be briefly explained. This circuit system constitutes an astable multivibrator, and one of transistors 17 and 18 is always on.
It is in the ON state. Transistor 20 and transistor 21 receive a control voltage input from control terminal 22.
It acts to flow a constant current I _O determined by V _d .
Note that the emitter resistor 23 of the transistor 20 and the emitter resistor 24 of the transistor 21 have the same resistance value, and if the resistance value is R _E , I _O is given by the following equation if the emitter resistor component inside the transistor is ignored.

I _O = V _d - V _BE /R _E (1) (V _BE : Voltage between the base and emitter of the transistor) The timing capacitor 19 is repeatedly charged and discharged by a constant current I _O. The charging/discharging time t is
Letting the capacitance of the timing capacitor 19 be C _O , it is expressed by the following equation.

t=2C _O V _D /I _O ......(2) (V _D : Voltage between anode and cathode when diodes 14 and 15 _are ON) Therefore, the oscillation frequency f _O is determined by equations (1) and (2). =1/2t=I _O /4C _O V _D ...(3) =1/4C _O V _D (V _d −V _BE /R _E ) ...(4). As shown in equation 4, the oscillation frequency f _O is proportional to the control voltage V _d . Note that it is obtained from the oscillation output terminal 16.

By the way, as shown in equation (3), the oscillation frequency f _O is also proportional to the collector current I _O of the transistor 20 and the transistor 21 . Therefore, if this current I _O is directly controlled, this circuit can become a current controlled oscillator.

FIG. 3 is a specific example of a circuit in which the VCO circuit shown in FIG. 2 is changed to a current controlled oscillator.

In the figure, a transistor 26 whose characteristics match those of the transistors 20 and 21 as much as possible is used;
The resistance value of the emitter resistor 27 is set to the same resistance value R _E as the resistors 23 and 24. With this configuration, transistor 26 and transistor 2
0, the transistor 26, and the transistor 21 form a mirror circuit, and the collector current of the transistor 20 and the collector currents of the transistor 20 and the transistor 21 have the same amount of current. Therefore, the control current I input from the input current terminal 17 is equal to the current I _O that charges and discharges the timing capacitor 19, so the oscillation frequency f _O is f _O = I/4C _O V _D ...(5) An oscillation output with a frequency proportional to the input control current I can be obtained.

As described above, the current controlled oscillator can be easily constructed by using an emitter-coupled multivibrator type VCO.

FIG. 5 shows a specific example of a voltage-current conversion circuit. In the figure, transistor 36 and transistor 37 constitute a differential amplifier. Further, the transistor 38 and the transistor 39 serve as a constant current load using a mirror circuit. In the figure, a voltage signal input from a voltage input terminal 33 is differentially amplified between a transistor 36 and a transistor 37.
The amplified current flows into and out of the collectors of transistor 36 and transistor 37. transistor 37
The collector current of transistor 3 is transmitted to the collector current of transistor 38 by a mirror circuit of transistor 39 and transistor 38.
6 and the collector current of the transistor 38 is output from the current output terminal 36. The resistance values of the emitter resistor 42 of the transistor 36 and the emitter resistor 43 of the transistor 37 are both
Assuming that R _e is a sufficiently large hfe of the transistor and that the emitter resistance inside the transistor can be ignored, the output current i is expressed by the following equation, where the input voltage is v.

i=v/R _e (6) As described above, the voltage-current conversion circuit can be configured with a relatively simple circuit.

In FIG. 5, 35 is a power input terminal of this voltage-current conversion circuit, transistor 40 is a transistor for generating a reference bias current, and 50 is a reference bias voltage input terminal. ON/OFF of operation of this voltage-current conversion circuit
To control this, it is sufficient to turn on and off the power supply applied to the power supply input terminal 35, or to turn on and off the bias voltage applied to the reference bias voltage input terminal.

A specific configuration of the present invention can be realized by using two voltage-current converters as described above, mixing their output current signals, and inputting the mixed current signal to a current-controlled oscillator.

Note that when mixing the output current signals of two voltage-current converters, since the signal is in a current state,
There is no need for a special adder or mixer, and the output current terminal of the voltage-current converter (Fig. 5-34) is directly connected to the circuit that supplies the bias current that determines the FM center frequency (Fig. 4-34). 3) and connect it to the input terminal of the current controlled oscillator (FIG. 3-17).

As explained above, current-controlled oscillators and voltage-current converters can be configured with relatively simple circuits, and if you use them to switch the VCO input signal as a current signal, you can achieve very high performance. A high-performance FM modulator and FM demodulator can be configured with one VCO.

Effects of the Invention In this way, the present invention allows an FM modulator/demodulator to be configured with a single VCO with a relatively simple circuit configuration, has a large dynamic range of signals that can be handled, and has a center frequency drift of the modulated signal. It has a large number of advantages, such as having high performance such as small size, and also being able to be integrated into an IC because it does not use mechanical switches.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of a conventional FM modulation/demodulation circuit, Figure 2 is an electric circuit diagram showing a specific example of a conventional VCO circuit, and Figure 3 is a specific example of a current controlled oscillator. Electrical circuit diagram, FIG. 4 is a block diagram showing an example of a specific configuration diagram of the current controlled oscillator of the present invention, and FIG. 5 is an electric circuit diagram showing a specific example of the voltage-current converter of the present invention. It is. 1...Modulation signal input terminal, 4...Switch, 5
...VCO, 6...FM modulation signal output terminal, 7...
FM modulation signal input terminal, 8...Limiter circuit, 9
... Phase comparator, 10 ... Low pass filter, 1
4, 15...diode, 17, 18, 20, 2
1, 26, 36, 37, 38, 39...transistor, 28, 29...voltage-current converter, 31...
...Current controlled oscillator, 30...Switch.

Claims (1)

[Claims] 1 first means for exchanging a first voltage signal into a first current signal by a first voltage-to-current converter;
second means for converting a second voltage signal into a second current signal by a second voltage-current converter; and a first current signal obtained by the first means;
a third means for adding the second current signal obtained by the second means; and a fourth means for driving a current controlled oscillator with the added current signal obtained by the third means. and a fifth means for controlling operation of either the first voltage-current converter or the second voltage-current converter.
A voltage controlled oscillator with an input switch, characterized by comprising two means.