JPH0453302A - Frequency conversion circuit for radio receiver - Google Patents

Abstract

PURPOSE:To reduce the oscillating frequency of a reference oscillator, to simplify the constitution of the oscillator and to facilitate integration of the circuit by setting each frequency, a frequency multiple ratio and a frequency division ratio so as to satisfy the specific condition. CONSTITUTION:Each frequency, a frequency multiple ratio M and a frequency division ratio N are set so that 1st and 2nd local oscillating frequencies fosc1, fosc2 fed respectively to 1st and 2nd frequency converters 1, 2 satisfy the condition of fosc1=foscXM and fosc2=fosc/N. Thus, the oscillating frequency fosc of a reference oscillator 3 is expressed as fosc=fosc1,fosc2/M(=fosc2XN) and then the frequency fosc is enough to be 1/M of the 1st local oscillating fosc1. Thus, the oscillating frequency fosc of the reference oscillator 3 is decreased and then the frequency conversion circuit of the double conversion system with simple circuit constitution and ease of circuit integration is realized.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to navigation systems using artificial satellites, mobile radios such as automobile radios and pagers, and radio communication systems using extremely high frequencies such as satellite communications. This invention relates to a frequency conversion circuit for a radio receiver.

[Conventional technology]

For example, the so-called GPS (Global Positioning System) is a positioning system that uses artificial satellites.
System) is known. This GPS has a total of 24 GPs, 4 each on 6 orbits orbiting the earth.
By launching an S satellite and receiving radio waves from at least three, preferably four, of these 24 satellites with a ground-based GPS receiver, the navigation data contained in the transmitted signal is used. It calculates the current position in real time.

Taking the case of the C/A code, which is open to the private sector, as an example, the frequency of the radio waves transmitted from the satellite in this GPS is as follows.
1575.42 MHz (-154Of, MHz
, fo is the transmission bit rate of C/A code 1.023 M
It uses an extremely high frequency (bps). When using extremely high frequencies like this, it is difficult to directly demodulate the received signal as it is on the receiving side; it is necessary to convert the received signal to a low frequency suitable for processing, and then perform demodulation and necessary processing. is normal.

FIG. 4 shows an example of a frequency conversion circuit of a conventional GPS receiver for frequency conversion. FIG. 4 shows an example of a so-called single conversion type frequency conversion circuit in which a frequency converter 43 lowers the received frequency 1540fo from a GPS satellite to a target intermediate frequency 4f.

On the other hand, in FIG. 5, the receiving frequency 154Of is lowered to the first intermediate frequency 260fo in the first frequency converter 53, and then lowered to the second intermediate frequency 4f in the second frequency converter 54. An example of a so-called double conversion type frequency conversion circuit is shown below.

[Problem to be solved by the invention]

In the case of the single conversion method shown in Figure 4, one frequency conversion lowers the target frequency to 4fo.
The circuit is very simple, but on the other hand, the image frequency is 1532 f 0 (=1536 f.

4fo), which is very close to the reception frequency 1540fo, so that the bandpass filters 41 and 42 can hardly remove this image frequency component.

Therefore, in the case of the single conversion method, a special frequency converter called an image removal mixer must be used as the frequency converter 43, which has the function of canceling the image frequency component by itself.

However, since this image removal mixer includes a phase shifter and the like, there are problems in that it is not only difficult to integrate, but also expensive.

Further, the local oscillation frequency 1536f supplied from the local oscillator 44 to the frequency converter 43 is the receiving frequency 1540f.
Since the frequency is high, close to o, it is very difficult to obtain a highly accurate oscillator in this frequency range. For this reason, a reference oscillator that oscillates at a relatively low frequency is usually used, and this frequency is multiplied by a frequency synthesizer to obtain a target local oscillation frequency.

Therefore, the circuit configuration becomes complicated and expensive.

On the other hand, in the case of the double conversion method shown in Figure 5, the frequency is lowered to an easier to process frequency by two frequency conversions.
Although the circuit configuration is more complicated than the single conversion method described above, the image frequency is converted to the receiving frequency 1.
L 02 Of , (-1
28Of. -26Of, ), and this image frequency component can be removed by a bandpass filter 5152 with a simple configuration. However, the local oscillator 55
The oscillation frequency must be as high as 1280fo in relation to the first intermediate frequency 260fO, and when integrated, there is a problem similar to that of the single conversion.

The present invention was made under the above circumstances, and its purpose is to provide a device that is less susceptible to image frequency interference, does not require special parts such as an image removal mixer, and has a simple circuit configuration. An object of the present invention is to provide a double-conversion type frequency conversion circuit that is easy to integrate.

[Failure to solve the problem]

As shown in FIG. 1, the frequency conversion circuit of the present invention includes a first frequency converter 1 that converts a received signal to a first intermediate frequency f
a second frequency converter 2 that converts IFI into a second intermediate frequency f IF2; a reference oscillator 3; and the reference oscillator 3.
The oscillation frequency f. sc is multiplied by M (M is an integer) and the first
A first local oscillation frequency f is applied to the frequency converter 1. 8,1, and the second frequency converter 2 which divides the oscillation frequency of the reference oscillator 3 by N (N is an integer).
and a second local oscillation frequency f. a frequency divider 5 supplied as SC2, and the difference between the frequency f5 of the received signal and the first intermediate frequency f IFI is the first intermediate frequency f I
The first and second intermediate frequencies fIFII f IF2 are selected such that the frequency is the difference between FI and the second intermediate frequency fIF2 multiplied by the frequency doubling ratio M and the frequency division ratio N, and Frequency f3 of received signal and first intermediate frequency f
The difference from IFI is the oscillation frequency fQ of the reference oscillator 3
equal to the frequency obtained by multiplying SC by the frequency multiplication ratio M, and the first intermediate frequency f IFI and the second intermediate frequency r
The difference from +r□ is the oscillation frequency f of the reference oscillator 3. s
The frequency is set to be equal to the frequency obtained by dividing c by the frequency division ratio N.

Note that as the first frequency converter 1, a reference oscillator 3
The first local oscillation frequency f is based on the zero oscillation output. SCI
The frequency doubler 4 can be omitted by using a harmonic-operated frequency converter in which the frequency is directly created within the converter itself.

[For production]

When the value of each frequency, the frequency doubling ratio M, and the frequency division ratio N are set so as to satisfy each of the above conditions, the first and second local frequencies supplied to the first and second frequency converters 1 and 2, respectively, are Oscillation frequency f. SCI y f 03CZ does not satisfy the following relationship.

f　osc+　=　(osc　X　M f　0SC2-f　. -c/N Therefore, the oscillation frequency f of the reference oscillator 3. ,.

is fosc = fosc+/M (= fosczX
N), and the first local oscillation frequency f. 1/M of SCI
frequency. As a result, the oscillation frequency of the reference oscillator for generating the local oscillation frequency can be lowered, and the oscillator does not need to have a special circuit configuration.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of a frequency conversion circuit for a GPS receiver configured to apply the present invention.

In this first embodiment, the first intermediate frequency f in the first frequency converter 1 is FI-10Of. , the second intermediate frequency f+rz=4fo in the second frequency converter 2, and the oscillation frequency f of the reference oscillator 3. 3c'''288fo, the frequency doubling ratio M of the frequency multiplier 4 is 5, and the frequency division ratio N of the frequency divider 5 is 3.

When each value is selected in the above relationship, the first local oscillation frequency f supplied to the first frequency converter 1. SCI is fosc
xM=288foX5=1440fo, and
The second local oscillation frequency f 05C2 supplied to the second frequency converter 2 is f osc /N=288f o
/ 3 = 96 fo.

According to this first embodiment, the oscillation frequency f of the reference oscillator 3. 3o can be reduced to 288fO of 115 of the first local oscillation frequency fosc +, and the image frequency in the first frequency converter 1 is 1
340f, (-1440f.-100fo), which is a value 2001o apart from the reception frequency 15/lof, and can be sufficiently removed by the bandpass filter 67.

FIG. 3 shows a second embodiment of the invention.

This second embodiment uses a harmonic-operated frequency converter 1 as the first frequency converter 1 in the first embodiment.
a. A so-called harmonic mixer is adopted, and the frequency multiplier 4
is omitted.

As is well known, a harmonic mixer is capable of generating a local oscillation frequency with a required frequency multiplication ratio by the conversion circuit itself using harmonic components of an input signal. therefore,
A first local oscillation frequency f having a frequency five times higher than the oscillation output of the reference oscillator 3. sc+= 1440 fo
By generating , the first frequency conversion can be performed without requiring the frequency doubler 4 in FIG. 2.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the oscillation frequency of the reference oscillator is multiplied by M to obtain the first local oscillation frequency, and the oscillation frequency of the reference oscillator is divided by N to obtain the second local oscillation frequency. The oscillation frequency of the reference oscillator is reduced to 1/M of the first local oscillation frequency by setting the values of each frequency, frequency doubling ratio M, and frequency division ratio N so as to satisfy certain conditions. Therefore, the configuration of the oscillator becomes easy and the integration of the circuit becomes easy.

Moreover, the image frequency in the first frequency converter is also
As in the case of the conventional double conversion method, since it can be sufficiently separated from the receiving frequency, it is less susceptible to image frequency interference, does not require special parts such as an image removal mixer, and can be constructed at low cost.

Furthermore, if a harmonic-operated frequency converter is used as the first frequency converter, a frequency doubler for generating the first local oscillation frequency can be omitted, and the circuit can be configured more simply. I can do it.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of the present invention, Fig. 2 is a block diagram of the first embodiment of the invention, Fig. 3 is a block diagram of the second embodiment of the invention, and Fig. 4 is a GPS reception FIG. 5 is a block diagram showing an example of the configuration of a conventional double-conversion frequency conversion circuit in a GPS receiver. 1.! - First frequency converter, 1a... Harmonic operated frequency converter, 2... Second frequency converter, 3...
・Reference oscillator, 4... Frequency doubler, 5... Frequency divider, fs
... Reception frequency, f IF+ ... First intermediate frequency, flF2 ... Second intermediate frequency, f 03CI・
...First local oscillation frequency, f oscz... Second local oscillation frequency, f osc... Oscillation frequency of the reference oscillator, M... Frequency doubling ratio, N... Frequency division ratio.

Claims (2)

[Claims] (1) a first frequency converter that converts a received signal to a first intermediate frequency; a second frequency converter that converts the first intermediate frequency to a second intermediate frequency; a reference oscillator; a frequency doubler that multiplies the oscillation frequency of the reference oscillator by M (M is an integer) and supplies the first local oscillation frequency to the first frequency converter; is an integer) and supplies the second local oscillation frequency to the second frequency converter as a second local oscillation frequency.
The first and second select an intermediate frequency, the difference between the frequency of the received signal and the first intermediate frequency is equal to the oscillation frequency of the reference oscillator multiplied by the frequency multiplication ratio M, and the difference between the first intermediate frequency and the first intermediate frequency; A frequency conversion circuit for a radio receiver, characterized in that a difference from a second intermediate frequency is equal to a frequency obtained by dividing the oscillation frequency of the reference oscillator by the frequency division ratio N. (2) In the frequency conversion circuit for a radio receiver according to claim (1), as the first frequency converter, the first local oscillation frequency is directly created within the converter itself based on the oscillation output of the reference oscillator. A frequency conversion circuit for a radio receiver, characterized in that it uses a harmonic-operated frequency converter and omits a frequency multiplier.