JPH0426206A - Modulator and pll frequency synthesizer using said modulator - Google Patents

Abstract

PURPOSE:To make a frequency characteristic flat and to suppress the deviation of the maximum frequency within a rated value by parallelly connecting a low-pass filter to a varactor diode which inputs a modulating input signal and modulates a carrier frequency signal. CONSTITUTION:In a modulation circuit 10, a low frequency input terminal 9 for sound modulation is connected through resistors 12 and 13 to the anode terminal of a varactor diode 11 for modulation and connected to the input terminal of a low-pass filter 8. The output terminal of this low-pass filter 8 is connected through a capacitor 17 for cutting a direct current to the cathode terminal of the varactor diode 11 for modulation. Therefore, the low-pass filter 8 parallelly connected to the varactor diode 11 for modulation loads the modulation of a phase inverse to that of the said varactor diode for modulation, and a peaking characteristic generated in the low area of a sound frequency band is canceled. Thus, the frequency characteristic of the PLL frequency synthesizer is made flat, and the deviation of the maximum frequency is suppressed within the rated value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a modulation device, and particularly to a modulation device suitable for use in a transmitter in a wireless telephone device such as a car telephone or a cordless telephone.

[Prior Art] Figure wi4 shows a schematic configuration of a transmitter using a PLL frequency synthesizer with a conventional modulation device.

The transmitter shown in the figure amplifies the output frequency signal of the modulation device in a transmission amplification circuit 2 and transmits it from an antenna 1.

The PLL frequency synthesizer includes a voltage controlled oscillator circuit 3 that outputs a frequency signal according to an input voltage, a variable frequency divider circuit 4 that divides the output frequency signal of the voltage controlled oscillator circuit 3, and an output of a reference frequency generator 115. The phase of the reference frequency signal output from the variable frequency divider circuit 4 is compared with the divided frequency signal output from the variable frequency divider circuit 4, and the voltage HfllRm is outputted via the loop filter 6.
and a phase comparator circuit 7 for controlling the output shoulder wave number of the F path 3.

First, the general operation of the transmitter will be explained.

When the transmitter (not shown) is turned on and the frequency division value in the variable frequency circuit 4 is changed appropriately to specify the transmission frequency,
The same town variation j11 times JII4 divides the oscillation output frequency signal of the voltage controlled oscillation circuit 3, and the divided frequency signal is inputted to one input terminal of the phase comparison port 176.
The other input terminal of the phase comparison circuit 7 receives a highly stable reference frequency signal output from the reference frequency generation circuit 5, and the phase comparison circuit 7 compares the phases of both signals. The phase difference signal is input to the voltage controlled oscillation circuit 3 via the loop filter 6.

This becomes a tuning voltage signal in the voltage controlled oscillation circuit 3.

That is, by feedback-controlling the output frequency of the voltage controlled oscillation circuit 3 using a highly stable reference frequency signal as a reference, the frequency stability of the frequency signal transmitted via the transmission amplifier circuit 2 and the antenna 1 is increased. There is.

Next, the modulation circuit in this transmitter will be explained.

When an audio signal is input to the low frequency input heir 9 in the variable 11 circuit 10 via a microphone or a low frequency li@ path.

The voltage of the same signal is divided by resistors 12 and 13, and the divided voltage value is input to the anode terminal of the modulating varactor diode 11. Since the cathode terminal of the modulating varactor diode 11 is connected to the resonant circuit in the voltage controlled oscillation circuit 3, the voltage controlled oscillating circuit 3 is activated by the audio signal input to the anode terminal of the modulating varactor diode 11.
FM modulation is applied directly to the output frequency signal. In addition,
The capacitor 14 is a bypass capacitor for high side wave signals, and grounds the anode terminal of the modulating varactor diode 11 at high frequencies.

By the way, the transmission rise time from turning on the transmitter and specifying the transmission frequency channel until the transmission frequency stabilizes, and the transmission frequency when changing the frequency from one channel to another. The channel switching time until stabilization is determined by loop filter 6.
change depending on the time constant of In order to shorten the transmission rise time and channel switching time, the number of time chambers of the same loop filter 6 can be reduced, but in that case, the frequency characteristics are as follows.
As shown in ll51m, 300 Hz ~ 3000H
It will have a peaking characteristic in the low range of the audio frequency band of z, and will not be flat, and the maximum frequency deviation will also exceed the specified value in the low range of the audio frequency band.

[Problems to be solved] The conventional PLL frequency synthesizer mentioned above.

When attempting to shorten the transmission rise time and channel switching time, there was a problem in that the single frequency characteristic did not become flat.

Further, there was a problem in that the maximum frequency deviation also exceeded the specified value in the low range of the audio frequency band.

The present invention has been made in view of the above-mentioned problems, and it is possible to achieve flat frequency characteristics in a PLL frequency synthesizer, keep the maximum frequency deviation within specified values, and shorten the transmission rise time and channel switching time. The purpose of the present invention is to provide a possible modulation device.

[Problem Solver R] In order to achieve the above object, the invention claimed in Ill provides a modulation device that modulates a carrier frequency signal by including a modulation varactor diode into which a modulation input signal is input. It has a configuration in which a low-pass filter is connected in parallel to a varactor diode.

In addition, the invention according to claim 112 includes 2: oscillation means having a modulation circuit made of a modulation varactor diode to which a modulation input signal is input, frequency division means for dividing the frequency signal output from the oscillation means, and a reference. A reference frequency oscillation means for outputting a frequency signal, inputting the eight frequency signals of the frequency dividing means and the reference frequency oscillation means, and performing a phase comparison;
The oscillation 4I! in the oscillation means is transmitted through the loop filter.
The PLL frequency synthesizer is equipped with phase comparison means for controlling the R wave number, and has a configuration in which a low-pass filter is connected in parallel to the modulating varactor diode.

[Function] In the inventions according to the first and twelfth claims configured as described above, the low-pass filter connected in parallel with the variable 11M varactor diode applies modulation in the opposite phase to the modulating varactor diode. , cancels out the peaking characteristics that occur in the low frequency range of the audio leakage frequency band.

[Example code] Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 11 shows a modulation device according to an embodiment of the present invention.
A schematic configuration of a transmitter using an LL frequency synthesizer is shown. Note that parts common to or corresponding to those of the conventional example are denoted by the same reference numerals.

In the figure, a voltage controlled oscillation circuit 3 in a PLL frequency synthesizer connects a modulation circuit 10 having a modulation varactor diode 11 between a resonance circuit 20 and an oscillation layer transistor circuit 40, and also connects an output of the oscillation transistor circuit 40. A buffer amplifier 50 is connected to the side thereof.

Furthermore, the low frequency input terminal 9 for audio modulation in the modulation circuit 10 is connected to the anode terminal of the modulation varactor diode 11 via a resistor 12.13, and is also connected to the input terminal of the low pass filter 8. In addition, the output terminal of the low-pass filter 8 is connected to the capacitor 1 for cutting DC.
7 to the cathode terminal of the modulating varactor diode 11. A series circuit consisting of resistors 15 and 16 applies a reverse bias voltage to the cathode of the modulating varactor diode 11, and a bypass capacitor 14 grounds the anode terminal of the modulating varactor diode 11 at high frequency. Since the cathode terminal of the modulating varactor diode 11 is connected to the resonant circuit 20 of the voltage controlled oscillation circuit 3 and the oscillation transistor circuit 40 by the coupling capacitor 31, when an audio signal is input to the low frequency input terminal 9, Direct FM conversion is applied.

A resonant circuit 20 in the voltage controlled oscillation circuit 3 includes an inductor 21, capacitors 22 and 23, and a varactor diode 2.
4, the voltage output from the loop filter 6 controls the capacitance of the varactor diode 24 in order to tune the oscillation frequency of the voltage controlled oscillation circuit 3, and the output signal of the resonant circuit 20 is coupled. Oscillation transistor circuit 4 in voltage controlled oscillation circuit 3 via capacitor 32
The signal is input to the drain of a field effect transistor 41 provided in 0.

Oscillation transistor circuit 4 in voltage controlled oscillation circuit 3
o creates a negative resistance at the oscillation frequency of the voltage controlled oscillation circuit 3, and the resonant circuit 20 is connected via the field effect transistor 41, the source resistor 44, the oscillation capacitors 42 and 43, and the coupling capacitor 32. An oscillation circuit is constructed, and a power supply voltage is supplied to the drain of a field effect transistor 41 via a choke coil 45. Capacitor 46 is a high frequency bypass capacitor.

The output signal of the oscillating transistor circuit 40 is input to a buffer amplifier 50 via a coupling capacitor 47.

In the above configuration, when an audio signal is input to the low frequency input terminal 9 of the modulation circuit 10 via the microphone or the low frequency circuit,
The audio signal is voltage-divided by resistors 12 and 13 and input to the anode terminal of the modulating varactor diode 11, so that it is directly subjected to FM modulation.

By the way, the cutoff frequency of the low-pass filter 8 is
As shown in the lfZ diagram, since the frequency characteristic of the conventional PLL frequency synthesizer is selected near the peak point, the frequency band below the cutoff frequency of the low-pass filter 8 among the audio signals input to the low-frequency input terminal 9 is selected. The component passes through the same low-pass filter 8 and is input to the cathode terminal side of the modulating varactor diode 11. As a result.

Correct with the modulation by the audio signal input to the anode terminal and in opposite phase! iFM modulation will be applied.

Therefore, if the level input to the cathode side of the modulating varactor diode 11 at the input or output of the low-pass filter 8 is properly adjusted, the modulation frequency characteristics will interfere with each other, resulting in peaking as shown in Figure 3. It becomes a flat object with no characteristics.

Note that even if the low-pass filter 8 is connected.

The audio signal for the band above the cutoff frequency is attenuated by the same low-pass filter 8, and is not input to the cathode terminal side of the modulating varactor diode 11.
Therefore, for the band above the cutoff frequency of the low-pass filter 8, the frequency characteristics are no different from those of the conventional one.

[Effects of the Invention] As explained above, in the present invention, the low-pass filter connected in parallel with the modulating varactor diode applies modulation that cancels out the peaking characteristics occurring in the low range of the audio frequency band, so the PLL frequency The present invention has the advantage that it is possible to provide a variable II device in which the frequency characteristics of the synthesizer are flat, the maximum shoulder wave number deviation is within a specified value, and the transmission rise time and channel switching time can be shortened.

[Brief explanation of the drawing]

FIG. 111 shows a P having a modulation device according to an embodiment of the present invention.
A block diagram of a transmitter using a LL frequency synthesizer, Figure 112 is a frequency characteristic diagram of a low-pass filter, II1
3rM is a frequency characteristic diagram of the transmitter shown in Figure 11, IF5 is a block diagram of a transmitter using a PLL frequency synthesizer with a conventional modulation device, and Figure 5 is a frequency characteristic diagram of the transmitter shown in IF5. be. 3: Voltage controlled oscillator circuit 4: Variable frequency divider circuit 5: Reference frequency generation port j16: Loop filter 7: Phase comparison port j
! 8: Low pass filter 9: Low frequency input terminal 1
0: Modulation circuit 11: Modulation varactor diode

Claims (2)

[Claims] (1) A modulation device that modulates a carrier frequency signal and includes a modulation varactor diode to which a modulation input signal is input, characterized in that a low-pass filter is connected in parallel to the modulation varactor diode. (2) An oscillation means having a modulation circuit consisting of a modulation varactor diode into which a modulation input signal is input, a frequency division means for dividing the frequency signal outputted by the oscillation means, and a reference frequency oscillation means for outputting a reference frequency signal. and phase comparison means for inputting the frequency signals output from the frequency dividing means and the reference frequency oscillation means, performing a phase comparison, and controlling the oscillation frequency in the oscillation means via a loop filter. A PLL frequency synthesizer characterized in that a low-pass filter is connected in parallel to the modulating varactor diode.