JPS622720A - Frequency synthesizer - Google Patents

Abstract

PURPOSE:To decrease the number of surface acoustic wave voltage control oscillators SAW-VCO by driving selectively the SAW-VCO which satisfies desired oscillation frequency in consideration of the variation of an oscillation frequency range owing to the temperature in a working mode. CONSTITUTION:A temperature sensor 8 consisting of a temperature-sensitive element like a thermistor, etc. is newly provided in addition to a reference signal generator 1, a phase comparator 2, a loop filter 3, the SAW-VCO 4A-4N, a variable divider 5, a selection command circuit 6 and a changeover switch 7. The oscillation frequency range of the SAW-VCO 4A-4N is set at 5MHz respectively. Thus each SAW-VCO has the + or -1.728MHz change of the oscillation frequency range centering on +20 deg.C owing to the frequency temperature characteristics when those SAW-VCO are actuated in a -40 deg.C-+80 deg.C temperature range. Thus, the SAW-VCO 4A-4N which have oscillations 795-800MHz, 800-805MHz, 805-810MHz and 810-815MHz respectively at +20 deg.C have the oscillation frequency ranges as shown in a table 1 with each working temperature limit of -40 deg.C and +80 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a frequency synthesizer using a plurality of voltage controlled oscillators constituted by surface acoustic wave resonators.

[Technical background of the invention]

Today, voltage controlled oscillators are used in frequency synthesizers, etc.
A surface acoustic wave resonator (Surface Acoustic Wave Resonator) is used as an oscillation element constituting a llator (hereinafter abbreviated as VCO).
Stic Wave Ra5onator: SA
(abbreviated as W Kyōtsuko) is attracting attention.

Figure 3 shows one VC configured by this SAW resonator.
This is an example of a frequency synthesizer using O@, reference signal generator 1, phase comparator 2, Lu! 74k
l A 3.5AW-VCO 4 and a variable frequency divider 5 are provided. The reference signal output from the reference signal generator 1 is input to a phase comparator 2, and fed back to the phase comparator 2 through the variable frequency divider 5 at a specified frequency division ratio.
The output of the W-VCO 4 and the phase difference are compared. The comparison result of the phase comparator 2, that is, the phase difference output, is inputted to the 5AW-VCO 4 as a control voltage through the Roog filter 3.

Here, the 5AW-VCO 4 outputs a signal with a frequency that eliminates the phase difference according to the control voltage input from the Roog filter 3. By performing such control operation while arbitrarily varying the frequency division ratio of the variable divider 5, the output terminal T. An output signal of a desired frequency is obtained at ut. By the way, the above-mentioned SAW resonator has a high C/N ratio (Carrler-to-Noise P
Although it is excellent in terms of higher ratio) and low current consumption 76, it also has the characteristic of being difficult to maintain modulation sensitivity. As a specific example, the modulation sensitivity in the 400 PvfHz band is approximately I MHz/V, and when considering this condition for a 5AW-VCO with an operation control voltage range of 4V, 4 MHz oscillation in the 400 MHz band This means that only the frequency range can be covered. For this reason, in response to the demand for a frequency synthesizer capable of a wider oscillation frequency range, conventionally, as shown in Fig. 4, multiple 5AW-VCs to which each consecutive oscillation frequency range is individually assigned
The above requirements were met by using O4a-4n. That is, in the frequency synthesizer shown in FIG. 4, in response to a request to output a signal of a desired frequency, the selection command circuit 6 issues a command to the variable frequency divider 5 and the changeover switch 7 to set a frequency division ratio corresponding to the frequency. By giving a selection command for 5AW-VCO 4a to 4n whose oscillation range is the frequency concerned and driving the selected 5AW-VCO 4a to 4n with a division ratio set based on the command, an output signal of the desired frequency is generated. Output terminal T. u
I try to get it in time. In this way, multiple 5AW-V
In a frequency synthesizer that obtains a wide oscillation frequency range by using Co4a to 4n, the 5A
When selecting the number of W-VCOs 4a to 4n, the frequency-temperature characteristics of the SAW resonators have a significant influence.

That is, the SAW resonator has a linear frequency temperature characteristic, and the specific value is -28.8X 103Hz.
/l has been confirmed.

The influence of such frequency temperature characteristics on one 5AW-#CO is as follows: oscillation frequency range: 5 MHz, operating temperature range: -40 MHz
When considering 5AW-VCO from ℃ to +SO℃, Kono 5A
W-VCO is ±1.728[:(
-28,8X103)Hz/℃X(60℃℃)
This results in an increase or decrease in the oscillation frequency range of MHz. Therefore, when operating within the above operating temperature range (-40°C to +80°C), one 5AW-VCO can be used without being affected by the temperature.
The oscillation frequency range of
MHz, so in order to construct a frequency synthesizer that can cover an oscillation frequency range of 10 MHz in the 800 MHz band using this 5AW-#COt-, for example, seven (10 MHz / 1.544 M
Hz #6.5) of 5AW-VCO4a~4g was required.

[Problems with background technology]

Conventionally, in a frequency synthesizer that attempts to secure a wide oscillation frequency by using a plurality of 5AW-VCOs, each of the 5AW-VCOs is selectively driven according to a single condition of frequency. Therefore, the oscillation frequency range that can be used for one 5AW-VCO is limited to an extremely narrow range after subtracting the variation within the above operating temperature range due to the frequency temperature characteristics of the SAW resonator, making it possible to secure a wide oscillation frequency. In order to construct a frequency synthesizer, there are problems in that a large number of 5AW-VCOs are required, resulting in an increase in size and a rise in manufacturing costs.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and provides a frequency synthesizer that can ensure a wide range of oscillation frequencies, requires as few 5AW-VCo0 as possible, contributes to miniaturization of external shape, and reduction in manufacturing costs. The purpose is to

[Summary of the invention]

Therefore, in the present invention, a temperature sensor is newly provided, and based on the two conditions of the temperature detected by the temperature sensor and the desired oscillation frequency, five
The AW-VCO is selectively driven, and the sAw-VCO is determined by determining the 5AW-VCO to be driven after determining the oscillation frequency range of the 5AW-VCO at the detected temperature. This makes it possible to make maximum use of the oscillation frequency range within the above-mentioned operating temperature range.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a professional diagram showing one embodiment of a frequency synthesizer according to the present invention, including a reference signal generator 1,
Phase comparator 2, Ruder filter 3.5AW-VCO4A
~4N, in addition to the variable branch unit 5, selection command circuit 6, and changeover switch 7, a temperature sensor 8 consisting of a temperature sensing element such as a thermistor is newly provided. Let us consider the operation of a frequency synthesizer having such a configuration under the same conditions as the conventional one, that is, when an oscillation frequency range of 10 MHz in the 800 MHz band is required. Here, when each of the 5AW-VCOs 4A to 4N has an oscillation frequency range of 5 MHz and is operated in a temperature range of -40°C to +80°C, each of the 5AW-VCOs 4A to 4N has an oscillation frequency range of +20°C due to the frequency-temperature characteristics described above. Centered around ±
It has a variation width in the oscillation frequency range of 1.728 MHz.

Therefore, for example, 795-800 respectively at +20°C.
MHz, 800-805 MHz, 80!
y=810MHz, each 5AW-VCO48~4D oscillating 810~815MHz is -40℃ and +8
At each operating temperature limit of 0° C., each device oscillates within the oscillation frequency range shown in the table below.

FIG. 2 is a concrete diagram of how the oscillation frequency range varies depending on the operating temperature. As is clear from the above table and FIG.
The oscillation frequency range of 5 MHz each assigned to ~4 N is 1 when the minimum operating temperature limit is -40°C [Fig. 2 (a)] and from +20°C [Fig. 2 (b)]. .728 MHz increments and the corresponding 5AW-V
The total oscillation frequency range that can be secured by CO4A~4N is 7
It fluctuates from 96.728 to 816.728 h, and conversely, when the maximum operating temperature limit is +80°C [Figure (C)]
The total oscillation frequency range is 793.272 by moving down by 1.728 MHz from +20°C.
~813.272MHz. Considering this over the operating temperature range -40°C to +80°C, the EA
The total oscillation frequency range that can be secured by W-VCO4A to 4N is 796.728 to 813.272 MHz, so
The above-mentioned 800
10 MHz in the MHz band (800-810 MHz
) can cover the oscillation frequency range. For example, if you want an output signal with an oscillation frequency of 801 MHz, if the operating temperature is +20°C, select 95
This can be handled by selecting AW-VCo 4B [see figure (b)], but when the operating temperature is 140°C, 5AW-#CO4A must be selected by selection () [see figure (b)]. a)]. Also, when the operating temperature is +80c, 5AW-VCo
4 It is sufficient if B is selected [Figure (C)]. Similarly, in order to obtain an output signal with an oscillation frequency of 809 MHz, when the operating temperature is +20°C and -40°C, select 5AW-VCO4C using selections ■ and ■ ((b) and (,) ), operating temperature +
When the temperature is 80 DEG C., by selecting the 5AW-VCO4D using selection (2) [FIG. 4(C)], the output signal with the oscillation frequency of 809 MHz can be obtained. As a specific control operation, for example, based on the temperature detected by the temperature sensor 8 and the desired oscillation frequency, select 5AW-VCO 4A sufficient to obtain the oscillation frequency at the temperature on the table of the selection command circuit 6. -4N selection conditions and the setting conditions for the division ratio of the variable frequency divider 5 are calculated, and the changeover switch 7 and the variable division divider 5 are operated according to the calculated conditions, thereby achieving the set division ratio. By driving the selected SAW'VCO, an output signal of the desired oscillation frequency is output to the output terminal T. I'm trying to get it right. In addition, on the upper side, the oscillation frequency range is 795 to 800 MHz and 8, respectively, at an operating temperature of +20°C.
00~805MHz, 805~810MHz, 810~
5AW-VCO4A as divided into 815 MHz
~10 in the 800 MHz band because we prepared ~4N.
In order to secure the oscillation frequency range of MHz, the above four
AW-VCOJ A~4N was required, for example,
800~805 MH respectively at minimum operating temperature -40℃
z.

If you prepare three 5AW-VCOs with oscillation frequency ranges of 805-810MHz and 810-815MHz, each of these 5AW-VCOs will have a maximum operating temperature of +80
796.544 to 801.544M respectively at °C
Hz, 801.544-806.544MHz, 806
．． Since it oscillates from 544 to 811.544 MHz, the oscillation frequency range in the operating temperature range -40℃ to +80℃ is 79.
6.544~811.544MHz, at least 10 in the 800MHz band with these three 5AW-VCOs.
This means that the oscillation frequency range of ME(z (800 to 810 MHz)) can be secured.

[Effects of the Invention] As explained above, according to the frequency synthesizer of the present invention, the 5AW-VC which satisfies the desired oscillation frequency after taking into account the fluctuation of the oscillation frequency range due to the temperature during operation.
Since the 5AW-vCO is selectively driven, compared to the conventional frequency synthesizer that selectively drives the fiSAW-vCO based on a single condition of only the oscillation frequency, the 5AW-vCO is selectively driven.
The oscillation frequency range of o can be used more widely, and the number of 5AW-VCOs used to construct a frequency synthesizer that can secure a wide oscillation frequency range can be as small as possible. It has the excellent advantage of being particularly useful for reducing manufacturing costs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a frequency synthesizer according to the present invention, FIG. 2 is a schematic diagram showing how the oscillation frequency range varies with operating temperature in this frequency synthesizer, and FIGS. Each figure is a block diagram showing an example of the configuration of a conventional frequency synthesizer, and FIG. 5 shows each 5A in the frequency synthesizer shown in FIG.
It is a conceptual diagram showing the oscillation frequency range shared by W-vCO. 1... Reference signal generator, 2... Phase comparator, 3...
・Loop filter, 4, 48~4n, 4A~4N...
5AW-VCo, 5... variable branching unit, 6...
Selection command circuit, 7... changeover switch, 8... temperature sensor.

Claims (1)

[Claims] A plurality of voltage-controlled oscillators that are composed of surface acoustic wave elements and to which successive different oscillation frequencies are individually assigned, a temperature sensor that detects the environmental temperature during operation of the voltage-controlled oscillator, and a temperature detected by the temperature sensor. Based on the temperature, the variation in the oscillation frequency range of the voltage controlled oscillator is calculated, and the voltage controlled oscillator having the oscillation frequency range corresponding to the desired oscillation frequency is selected under the calculated variation conditions. A frequency synthesizer comprising: a control means for driving the frequency synthesizer.