JP2631018B2 - High frequency PLL oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a phase comparator, a voltage controlled frequency oscillator
VCO), high-frequency PL composed of a mixer and having a PLL
L oscillator. More specifically, in a PLL oscillator composed of a phase comparator, a VCO, and a mixer, an amplifier that amplifies the signal level is provided on the input side of the mixer, and the PLL oscillator loses lock due to spurious generated by the characteristics of the mixer. A high-frequency PLL oscillator including a limiter for controlling the amplitude of the output of the amplifier in order to prevent the occurrence of

[Conventional technology]

Wireless communication has made remarkable progress along with wired communication. Since long-distance communication requires enormous cost in wired communication, wireless communication is attracting attention again. Unlike wireless communication, wireless communication enables communication between a transmitting device and a receiving device without the need to lay a transmission path, and the need for wireless communication can be increased even in an environment where temperature changes rapidly. ing. In addition, mobile radios such as car phones, personal radios, pagers, and the like have recently become widespread. In the wireless communication developed in this manner, it is necessary to allocate and use frequency bands. However, since the frequency band is limited, the number of communication channels cannot be increased unnecessarily. In wireless communication used in a state where the frequency channel of such communication is congested, a device that uses a PLL oscillator and can transmit and receive at a wideband and accurate frequency is indispensable. The present invention aims to improve the performance of a PLL oscillator used in such a wireless communication device.

Conventionally, in a high-frequency PLL oscillator having a PLL, when used at a high frequency, a mixing-type PLL oscillator that mixes the oscillation frequency of a VCO with a local oscillation frequency, lowers the frequency, and inputs the frequency to a subsequent circuit has been considered. .

[Problems to be solved by the invention]

An object of the present invention is to realize a high-frequency oscillator having a wide band and a high frequency accuracy by a single PLL circuit without using a plurality of PLL circuits. In order to operate a single loop circuit in a phase-locked state over a wide area at a high frequency, mixing of a number of stages larger than three faces the following problem.

In other words, high-frequency PLL oscillators employ the mixing-down method that introduces a mixer, but when using a mixer that is an analog device, problems such as the PLL oscillator not functioning due to temperature changes occur. Will come. Hereinafter, the problem will be described.

Although the value changes depending on the type of element used, the signal input to the mixer at a low temperature is somewhat lower than that at a normal temperature. This is mainly due to the fact that the density of electrons is reduced inside the semiconductor element used to generate a signal, and the current flow is deteriorated as compared with that at normal temperature. When the level of the signal input to the mixer decreases, the level of the signal output from the mixer also decreases, so that the subsequent subsequent circuits do not operate. That is, since a three-stage mixer is used, the signal level is reduced by about 9 dB at the stage of input to the phase comparator. When the signal level decreases, the subsequent circuit does not operate due to the insufficient input signal level. In order to prepare for the decrease in the level of the signal input to the mixer at the time of low temperature, a measure may be considered in which an amplifier is provided before the mixer to increase the level of the input signal of the mixer.

However, if an appropriate signal level is set at a low temperature due to such measures, the input signal level in a normal state becomes excessive at a normal temperature, and spurious is generated from the mixer itself. As a result, malfunctions due to spurs occur in the subsequent circuit. Conversely, if the signal level is set to an appropriate level at normal temperature, the PLL oscillator will not operate normally due to a decrease in the signal level at low temperature.

In the case of a PLL oscillator using three or more mixers, since the level of the signal output from each mixer fluctuates due to a temperature change, the level fluctuation of the signal input to the final mixer becomes larger, resulting in frequency division. The instrument malfunctions.

[Means for solving the problem]

According to the present invention, a plurality of mixers having more than three stages are incorporated in a single PLL circuit and operated at different local oscillation frequencies. The amplitude control means is incorporated in a PLL circuit that covers the loss of signal amplitude lost by an analog device called a mixer with an amplifier. The inventor is convinced that the technical idea is completely new. According to an experiment, the amplitude control means (limiter) used in the above-mentioned method is merely a means for suppressing the amplitude, and need not be a soft limiter as disclosed in JP-A-62-274996. May be simple using non-linear element saturation.

In order to solve the above problems, in the present invention, in a PLL oscillator, an input signal to the mixer is amplified by an amplifier, and a limiter is provided before the mixer in order to suppress spurious generated from the mixer. Limit the level of the input signal. With such a configuration, the sensitivity of the subsequent circuit does not become insufficient at a low temperature, and the PLL oscillator operates normally at room temperature without an operation failure of the subsequent circuit due to spurious.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The conventional PLL oscillator shown in FIG. 4 comprises a phase comparator 1, a VCO 2 and a mixer 3.

FIG. 1 is a block diagram showing the configuration of a PLL oscillator according to the present invention. Elements having the same functions as those of the configuration of the conventional PLL oscillator shown in FIG. 4 are denoted by the same reference numerals. A basic mixing-down type PLL oscillator controls a frequency by a DC voltage and a phase comparator 1 that outputs an error signal pulse proportional to a phase difference between an oscillation frequency of a reference oscillator and a feedback signal frequency from an output of the VCO2. It comprises a VCO 2 and a mixer 3 that mixes down at the frequency of the local oscillator. The PLL oscillator according to the present invention includes the amplifier 4 for amplifying the input to the mixer 3 in the above-described mixing-down type PLL oscillator, and is provided at the subsequent stage of the amplifier 4 to be input to the mixer 3. It is characterized in that it has a limiter 5 for reducing the signal level and reducing the level of spurious components from the mixer itself.

Further, one embodiment of the present invention shown in FIG. 2 is based on the configuration of the PLL oscillator of FIG. 1 and has a configuration in which a mixer is provided in a plurality of stages in a PLL oscillator used at a higher frequency. It is shown. This embodiment will be described below. First, a loop filter (hereinafter referred to as LF) that removes the high-frequency component of the error signal pulse output from the phase comparator 1 and integrates the error signal pulse into a DC control signal is added to the configuration of the present invention shown in FIG. Abbreviation) 6 was added, and the mixers were arranged in multiple stages. That is, the first, second, and third mixers 7, 8, and 9 are provided. The level of the signal provided with the amplifier 4 before the third mixer 9, which is the final mixer, was maintained, and the level of spurious components from the mixer itself was reduced by providing the limiter 5. The effect of the present invention is maximized by the configuration in which the amplifier 4 and the limiter 5 are provided in the third mixer 9, that is, in the stage preceding the final stage mixer. That is, when a plurality of mixers are used, the level fluctuation of the input signal to the third mixer 9 is maximized, so that there is an effect that the limiter 5 is provided in a stage preceding the third mixer 9.

In addition, there is an effect even when the amplifier 4 and the limiter 5 are provided not only in the preceding stage of the third mixer 9 but also in the preceding stage of the first mixer 7 and the preceding stage of the second mixer 8. Then, the amplifier 4 and the limiter 5 may be provided in a stage preceding all the mixers.

Further, another embodiment of the present invention shown in FIG. 3 is different from the embodiment shown in FIG. 2 in that a signal output from the third mixer 9 is programmed within a frequency limit which can be divided by a frequency divider. And a control unit 11 for changing the frequency of the local oscillator input to the mixer and the frequency division ratio of the frequency divider 10 in correspondence with each other.

With the configuration as in this embodiment, the frequency of the signal output from the PLL oscillator can be made variable over a wide band, so that it is possible to change the frequency range by changing only the frequency division ratio of the frequency divider 10. Thus, a wide range of frequencies can be scanned without deteriorating various characteristics such as a CN ratio.

〔The invention's effect〕

The high-frequency PLL oscillator according to the present invention includes at least three or more mixers, controls these mixers at different local oscillation frequencies, and adjusts the frequency division ratio of the frequency divider and the local oscillation frequency in accordance with the high-frequency frequency to be oscillated. Is provided, the frequency of the signal output from the PLL oscillator can be varied over a wide band, and a wide range of frequencies can be scanned without deteriorating the CN ratio.

High frequency with at least three-stage mixer according to the invention
According to the PLL oscillator, the amplifier and the limiter for compensating the operation are provided together with the mixer, so that the above-mentioned function can be sufficiently exhibited even in an environment with a large temperature change. Furthermore, by controlling the frequency division ratio of the frequency divider and the local oscillation frequency different from each other in accordance with this high frequency frequency to be oscillated, a high frequency PLL oscillator with high resolution and high speed switching can be obtained. Can be That is, at low temperatures, the level of the signal of the local oscillator of the mixer decreases, and as the number of mixers used increases, the signal level decreases. If the gain of the amplifier is increased in preparation for this, the level of the spurious component of the signal from the mixer increases at room temperature, and the PLL oscillator does not operate normally.However, by using the limiter, the signal input to the mixer is reduced. The level can be limited to reduce the level of spurious components.

In addition, the limiter itself is hardly affected by temperature because it is composed only of diodes.Therefore, it is possible to operate the PLL oscillator normally, reliably and stably even at low temperatures or in an environment where temperature changes rapidly. it can.

Further, the present invention prevents the level of the signal generated in the PLL oscillator from lowering, and also prevents the spurious of the signal generated from the mixer itself. A high-frequency PLL oscillator configured as described above can be used.

Furthermore, when a filter is used instead of a limiter, if a steep filter characteristic is to be obtained, a multi-stage filter is required, and a large number of coils and capacitors as its constituent elements are required. When a limiter is used, no coil or capacitor is required, so that the PLL oscillator can be downsized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a PLL oscillator according to the present invention. FIG. 2 is a block diagram showing the configuration of one embodiment of the present invention. FIG. 3 is a block diagram of an embodiment of a PLL oscillator having a frequency divider and a control unit and controlling the signals of the frequency divider and the local oscillator in correspondence with each other, and FIG. 4 is a conventional PLL oscillator. FIG. 3 is a block diagram showing the configuration of FIG. 1 ... Phase comparator, 2 ... Voltage controlled frequency oscillator, 3 ...
... mixer, 4 ... amplifier, 5 ... limiter, 6 ... loop filter, 7 ... first mixer, 8 ... second mixer, 9 ... third mixer, 10 ... frequency divider, 11 ... Control unit.

Claims (1)

(57) [Claims] 1. A phase comparator (1), a loop filter (6) for removing a high frequency component of an error signal pulse output from the phase comparator, integrating the error signal pulse, and converting the error signal pulse into a DC control signal; A voltage controlled frequency oscillator (2) that receives the output voltage from the loop filter and controls the frequency to oscillate, and at least three stages that receive the frequency signal from the voltage controlled frequency oscillator and mix the frequencies at different local oscillation frequencies. (7, 8, 9), an amplifier (4) provided on the output side of the previous stage mixer of the mixer, and an output of the amplifier to limit the amplitude of the final stage mixer. And a frequency divider (10) for dividing the output from the last-stage mixer and inputting the divided frequency to the phase comparator, and a divider corresponding to a high-frequency frequency to be oscillated. period High frequency and a frequency dividing ratio and the control unit for changing different local oscillation frequencies, respectively (11)
PLL oscillator.