JPS5926140B2 - frequency converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency converter suitable for use in a receiver for receiving a modulated carrier signal, particularly in an FM and PM receiver.

Currently used FM and PM receivers adopt a single or double superheterodyne reception method, and their standard configuration is to first amplify the received human signal from the antenna with a high-frequency circuit, and then amplify it with a local oscillator. The output is led to a mixing circuit where it is converted to an intermediate frequency.

In the case of the double superheterodyne reception system, the signal is further converted to a second intermediate frequency, and then passed through an intermediate frequency amplifier, a demodulator, and an audio wave amplifier to be taken out as an output. Currently, a crystal oscillator is used as a local oscillator, but this utilizes the stable mechanical natural vibration of a crystal plate through its piezoelectricity, and usually thickness shear vibration is used. The resonant frequency is inversely proportional to the plate thickness, so the higher the frequency, the thinner the plate must be.When using the fundamental mode, 2
The upper limit is about 5MH2. Therefore, if it is desired to realize a stable oscillator in a frequency band higher than this, it is necessary to perform overtone excitation or use a multiplier. In addition, these outputs contain frequency components other than the desired overtone, and if they are led directly to the mixer, problems such as spurious radiation may occur. Therefore, only the desired oscillation frequency components are sent before the mixer. A filter must be inserted to allow it to pass. On the other hand, a surface acoustic wave oscillator that combines a surface acoustic wave delay line and an amplifier can easily oscillate in the fundamental mode up to around 1 GH2, and therefore has the advantage of increasing the multiplier required when using a conventional crystal oscillator. There is no need for containers, filters, etc. Further, in conventional receivers, the local oscillation signal is guided to a mixer together with the received signal, and the difference frequency component (intermediate frequency signal) is taken out as an output.
An object of the present invention is to provide a new frequency conversion device in which the functions of the local oscillator and mixer described above are realized by a single amplifier and a surface acoustic wave delay line.

According to the present invention, a broadband amplifier and a surface acoustic wave delay line are connected to form a loop, and the phase and amplitude conditions of the loop are selected so as to oscillate at a predetermined frequency fe. A frequency conversion device is obtained by adding a signal of frequency fs (fs←fe) to the circuit in the middle of this loop to obtain a difference frequency signal of fs-fe. That is, according to this configuration, two frequency components fe and fs are added to the input end of the amplifier, and fs-fe is
This difference frequency signal component is obtained from the output terminal.

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of a frequency conversion device according to the present invention. In the figure, reference numeral 1 denotes a piezoelectric substrate, one principal surface of which is mirror-polished, and interdigital transducers 2 and 3 are disposed facing each other on this surface. These converters are connected to the input and output terminals of the amplifier 4. Now, when a certain electric signal is applied to the input terminal of the amplifier 4, the amplified electric signal is converted into a surface acoustic wave by the interdigital transducer 2, and the surface of the substrate 1 is The signal propagates in the direction of , reaches the interdigital transducer 3, where the surface acoustic wave signal is converted back into an electric signal by a piezoelectric reaction. This electrical signal becomes the input signal to the amplifier 4 again. Therefore, the amplifier 4
An oscillator can be realized by selecting amplitude conditions such that the degree of amplification is greater than the loss due to propagation and conversion of surface acoustic waves in the delay line including the interdigital transducers 2 and 3. The oscillation frequency is determined by φM+φE=2πn(
n=1, 2, 3,...) This is a frequency that satisfies (1).

In a surface acoustic wave delay line, n usually has a value of several tens to several hundreds, so it is possible to oscillate at an extremely large number of frequencies. It is possible to satisfy the above-mentioned swing width condition only in this case. Furthermore, even if the width condition is satisfied for oscillation at two or more frequencies, oscillation occurs only at frequencies where the insertion loss of the delay line is smaller. On the other hand, the output amplitude settles at a certain value determined by the nonlinear effect of the amplifier. This oscillator (the oscillation frequency is Fe) is externally connected to a frequency of 8 (F)
s+f') signal is added.

In FIG. 1, the voltage is applied to the power end of the amplifier 4 via the terminal 6. Then, due to the nonlinearity of the amplifier 4, a signal component having a frequency of 1 fs±Fe, which is the sum and difference of both frequency components, is included in the output. That is, according to this configuration, the functions of a local oscillator and a mixer can be simultaneously realized with one amplifier and one surface wave delay line. Moreover, as already mentioned, since the surface acoustic wave oscillator can easily oscillate in the fundamental mode up to 1 GHz, there is no need for a multiplier or filter, which is a great advantage in terms of miniaturization and cost reduction of the device. FIG. 2 shows another embodiment according to the invention.

Components corresponding to those in FIG. 1 are designated by the same reference numerals. In this configuration, a signal with a frequency Js is applied to the interdigital transducer 9 via the terminal 8, becomes a surface acoustic wave, propagates in the direction of the arrow 10, reaches the interdigital transducer 3, and is further transmitted to the amplifier 4.
reaches the input terminal of Converter 9 of course has a frequency F
The pitch of the electrodes is determined so that it has a maximum amplitude response at s, and the logarithm of the electrodes is determined so that it has a zero response at the so-called image frequency, which is just a mirror image of Fs with respect to the local oscillation frequency F2. . That is, the surface acoustic wave delay line composed of interdigital transducers 9 and 3 functions as a so-called front-end filter used in conventional reception. Therefore, the device can be further downsized. As described above, according to the present invention, it is possible to obtain a frequency conversion device using a surface acoustic wave delay line that has a simple structure, is easy to manufacture, and operates stably.

[Brief explanation of the drawing]

1 and 2 show an embodiment of the frequency conversion device according to the present invention, in which 1 is a piezoelectric substrate, 2, 3, and 9 are interdigital transducers, and 4 is an amplifier.

Claims (1)

[Claims] 1 A surface acoustic wave delay line including a broadband amplifier and an input/output electromechanical transducer on a piezoelectric substrate is connected to form a loop, and the phase and amplitude conditions of the loop are set at a predetermined frequency fl. In the oscillation circuit selected to oscillate, a frequency fs (fs≠fl
), and extracts difference frequency signal components fs to fl from the output terminal of the amplifier by utilizing the nonlinear operation of the amplifier.