JPS63131705A - Synthesizer modulation circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for an expensive reference oscillator and a frequency adjusting means by using a switch circuit so as to select a reference oscillation frequency generated from a reference oscillation circuit depending on the logic of a digital signal alternatively and supplying the frequency to a phase locked loop circuit. CONSTITUTION:A reference oscillator main body consists of a reference oscillation circuit 51 generating two kinds of reference oscillation frequencies set in advance and a switch circuit 53. The switch circuit 53 is turned on/off in response to the logic level of a digital signal to select the reference oscillation frequency generated from the reference oscillation circuit 51. Thus, the reference oscillator is constituted very inexpensively in comparison with an oscillator using a variable capacitor. Since the reference oscillation frequency is fixed in advance by a circuit constant of the oscillation circuit, it is unchanged depending on the signal level of the digital signal, resulting in obtaining a stable reference oscillation frequency and a circuit varying the signal level of the digital signal is not required.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement of a synthesizer modulation circuit used in a mobile radio to which a multi-channel access method is applied, for example.

(Prior art) Conventionally, there is a modulation circuit of this type as shown in FIG.
, a phase-locked loop (PLL) circuit consisting of a frequency divider (frequency division ratio 1/n) 2, a phase comparator (PD) 3 and a low-pass filter (LPF) 4, a reference oscillator 5 and a frequency divider (divider). The voltage controlled oscillator 1 is provided with a modulation input terminal 7, and a modulation signal is input to the modulation input terminal 7 to generate a signal generated from the voltage controlled oscillator 1. The transmission carrier frequency is changed. With such a configuration, if the reference frequency generated from the reference oscillator 5 is fR, then the output terminal 8 outputs a transmission signal obtained by frequency modulating the transmission carrier wave with a frequency of n/m fR using a modulation signal. That will happen.

However, when trying to perform FSK modulation by inputting a digital signal as a modulation signal, such a conventional modulation circuit cannot output a modulated carrier wave when a digital signal with continuous "H" or "L II" levels is input. The problem is that the frequency change is corrected by the P, 11 circuit and the frequency deviation becomes small, making it impossible to transmit digital signals.

Conventionally, therefore, the following circuits have been considered as synthesizer modulation circuits for digital signal transmission.

Figure 5 shows its configuration, in which a frequency controlled reference oscillator 5' is provided and a variable attenuator 9 is connected to its frequency υ control terminal.
A digital signal as a modulation signal is inputted via the . With such a configuration, when a digital signal is input to the modulation input terminal 7, the oscillation frequency of the voltage controlled oscillator 1 changes according to a change in the signal level of this digital signal, and at the same time, the oscillation frequency of the voltage controlled oscillator 1 changes. Since the reference oscillation frequency to be transmitted changes in accordance with the signal level of the digital signal, the frequency change of the transmission carrier wave is not corrected and is sent out as is, thereby making it possible to transmit the digital signal.

However, such conventional circuits have the following problems. That is, (1) Frequency control means using a varicap is generally used as the reference oscillator 5', but this type of voltage controlled oscillator 5' is expensive.

(2) Since this type of voltage controlled oscillator 5' generally has variations in modulation sensitivity, a variable attenuator 9 is essential for adjustment, which also increases the cost of the circuit.

Furthermore, it is difficult to obtain a stable reference oscillation frequency.

(Problems to be Solved by the Invention) As described above, the conventional circuit uses a reference oscillator using a varicap as a frequency control means, which makes the circuit expensive and reduces the stability of the reference oscillation frequency. However, the present invention focuses on this point and aims to provide a synthesizer modulation circuit that is inexpensive and has a highly stable reference oscillation frequency by eliminating the need for an expensive reference oscillator and frequency adjustment means. It is something.

[Structure of the Invention] (Means for Solving the Problems) The present invention, as shown in FIG. An input circuit A, a reference oscillation circuit B capable of generating a plurality of preset reference oscillation frequencies, and a switch circuit C that constitutes a reference oscillator together with the reference oscillation circuit B are provided. The reference oscillation frequency generated from the oscillation circuit B is selectively selected depending on the logic of the digital signal and is supplied to the phase-locked loop circuit.

(Function) As a result, the reference oscillator is composed of a general oscillation circuit that fixedly generates a plurality of reference oscillation frequencies, and a switch circuit that selects one from the plurality of reference oscillation frequencies. The circuit is cheaper than one that uses varicaps to variably control the oscillation frequency. In addition, each reference oscillation frequency generated from the reference oscillator is fixedly set in advance for each oscillator alone, so it remains constant regardless of the signal level of the digital signal. It can be output. Furthermore, since a means for adjusting the signal level of the digital signal is not required, the valve circuit can be made inexpensive.

(Embodiment) FIG. 2 shows the configuration of a synthesizer modulation circuit in an embodiment of the present invention. Incidentally, the same parts as in FIG. 5 are given the same reference numerals and detailed explanations will be omitted.

A digital signal input from the modulation input terminal 7 is supplied to the voltage controlled oscillator 1 via a low pass filter (LPF) 60. Here, the reason why the low-pass filter 60 is inserted is to suppress the generation of interference waves by removing high frequency components of the digital signal, thereby reducing the negative influence on other receivers.

On the other hand, the digital signal input from the modulation input terminal 7 is also supplied to the reference oscillator main body 50 as is. The reference oscillator body 50 includes a reference oscillation circuit 51 that generates two types of preset reference oscillation frequencies using a crystal oscillator 52 as an oscillation source, and a switch circuit that includes a transistor 54 that operates on and off according to the logic level of the digital signal. 53, this switch circuit 53
Accordingly, the reference oscillation frequency generated from the reference oscillation circuit 51 is alternatively selected.

With such a configuration, when a digital signal is input to the modulation input terminal 7, this digital signal is supplied to the voltage controlled oscillator 1 after high frequency components are removed by the low pass filter 60, thereby controlling the voltage. The transmission carrier frequency generated from the oscillator 1 is FSK modulated in accordance with the change in the logic level of the digital signal. In addition, the digital signal is transferred directly to the switch circuit 5 of the reference oscillator main body 50.
3 is also supplied. Then, this switch circuit 53
The transistor 54 is turned on and off according to the logic of the digital signal, and the reference oscillation frequency generated from the reference oscillation circuit 51 is switched according to this on and off operation. In other words, the reference oscillator main body 51 is a oscillator whose switching is controlled according to the logic change of the digital signal as a modulation signal.
Outputs two reference oscillation frequencies. Therefore, the PLL circuit performs frequency pull-in according to the reference oscillation frequency output from the reference oscillator main body 50, and as a result, the voltage controlled oscillator 1 outputs the FSK signal according to the logic level of the digital signal.
A modulated transmit carrier wave is output. Therefore, even if a digital signal with continuous "H" or L°' is input as a modulation signal, a transmission carrier wave that is FSK-modulated in accordance with the logic level of this digital signal can be obtained.

Note that the reference oscillation frequency output from the reference oscillator main body 50 is switched at high speed, so it contains many high frequency components that become interference waves, but these high frequency components are generated by the PLL circuit. As a result, the output terminal 8 outputs an FSK-modulated transmission carrier wave that does not contain any interference waves.

In this example, “H” or “L IT
Even if a continuous digital signal is input as a modulation signal, it is possible to obtain a transmission carrier wave that has undergone F S Kvlm, and the reference oscillator main body 50 can be used as a standard for generating a preset 211 class reference oscillation frequency. It is composed of an oscillation circuit 51 and a switch circuit 53, and the switch circuit 53 is turned on and off according to the logic level of the digital signal, thereby selecting the reference oscillation frequency generated from the reference oscillation circuit 51. Accordingly, the reference oscillator can be constructed at a much lower cost than an oscillator using a varicap. In addition, since the reference oscillation frequency is fixed in advance by the circuit constants of the oscillation circuit,
As a result, a stable reference oscillation frequency can be obtained because it does not change depending on the signal level of the digital signal.Furthermore, a circuit for varying the signal level of the digital signal can be eliminated, making the valve circuit inexpensive. be able to.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and for example, the configurations of the reference oscillation circuit and switch circuit, the configuration of the modulation input circuit, the configuration of the PLL circuit, etc. may be varied without departing from the gist of the present invention. It can be modified and implemented.

[Effects of the Invention] As detailed above, according to the present invention, a modulation input circuit that changes the transmission carrier frequency output from a voltage controlled oscillator of a phase-locked loop circuit based on a digital signal, and a plurality of preset A reference oscillation circuit capable of generating a reference oscillation frequency of By selectively selecting and supplying the signal to the phase-locked loop circuit according to the logic, it is possible to eliminate the need for an expensive reference oscillator and frequency adjustment means, thereby stabilizing the reference oscillation frequency at low cost. Therefore, it is possible to provide a synthesizer modulation circuit with high performance.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram showing the configuration of the present invention, FIG. 2 is a circuit block diagram showing the configuration of a synthesizer modulation circuit in an embodiment of the present invention, and FIG. 3 is a circuit configuration diagram of the reference oscillator main body of the same circuit. , 4 and 5 are circuit block diagrams of different conventional synthesizer modulation circuits, respectively. 1... Voltage controlled oscillator (VCO), 2.6... Frequency divider, 3... Phase comparator (PD), 4.60... Low pass filter (LPF), 7... Modulation input terminal, 8.
...Transmission carrier wave output terminal, 50...Reference oscillator main body,
51... Reference oscillation circuit, 52... Crystal resonator, 53
...Switch circuit, 54...Switching transistor. Applicant's agent Patent attorney Takehiko Suzue Figure 2 53 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] In a synthesizer modulation circuit that uses a phase-locked loop circuit to obtain a transmission carrier frequency modulated by a digital signal, a modulation input circuit that changes the transmission carrier frequency output from a voltage-controlled oscillator of the phase-locked loop circuit based on the digital signal. a reference oscillation circuit capable of generating a plurality of preset reference oscillation frequencies, and a reference oscillation frequency generated from the reference oscillation circuit that is selectively selected according to the logic of the digital signal to achieve the phase lock. A synthesizer modulation circuit comprising a switch circuit for supplying a signal to a droop circuit.