JPH0423850B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AM radio receiver that uses a phase locked loop to control the oscillation frequency of a voltage controlled oscillator.

Conventionally, an AM radio receiver using a phased loop has, as shown in FIG. 1, an antenna circuit 1, a high frequency amplification circuit 2, a mixing circuit 3, an intermediate frequency amplification circuit 4, a detection and low frequency amplification circuit 5, and,
Consists of a reference signal generation circuit 6 using a crystal oscillator, a reference divider 7, a programmable divider 8, a phase comparator 9, a low-pass filter 10, a voltage controlled oscillator 11 as a local oscillator, an antenna circuit 1 and a high frequency amplification circuit. The circuit 2 had a tuning circuit including a varactor diode 12 which is a variable capacitance element, and the voltage controlled oscillator 11 also included the varactor diode 12.

Then, by supplying the control voltage from the low-pass filter 10 to each of the varactor diodes 12 of the antenna circuit 1, the high-frequency amplifier circuit 2, and the voltage-controlled oscillator 11, and supplying the output signal of the voltage-controlled oscillator 11 to the mixing circuit 3, Broadcast signals were being received.

So, if the broadcast band is 522-1611KHz and the channel space is 9KHz, for example,
In order to receive a 522KHz broadcast signal, assuming that the intermediate frequency is 450KHz, the oscillation frequency of the voltage controlled oscillator 11 should be set to 522+450=972KHz.
However, the broadcast signal usually passes through the tuning circuit of the antenna circuit 1 and the high frequency amplification circuit 2 and then reaches the mixing circuit 3.
However, if there is no tuned circuit,
Even if the oscillation frequency of the voltage controlled oscillator 11 is set to 972KHz in an attempt to receive a broadcast signal of 522KHz, the broadcast signal of the image frequency of 972+450=1422KHz will also be received. Therefore, in order to guide only the frequencies near 522 KHz to be received to the mixing circuit 3, the conventional antenna circuit 1 and high frequency amplifier circuit 2 required a tuning circuit.

However, the resonant frequency of the tuned circuit must be changed depending on the receiving frequency, and for this reason,
A varactor diode 12 was required in each tuned circuit. That is, in conventional radio receivers, varactor diodes were always required at three locations. Moreover, the oscillation frequency of the voltage controlled oscillator 11 and the resonant frequencies of the tuning circuits of the antenna circuit 1 and high frequency amplifier circuit 2 must change in conjunction with each other, and in order to reduce tracking errors, each paractor diode had to use materials with uniform characteristics. Furthermore, the variable range of the paractor diode is the antenna circuit 1 and the high frequency amplifier circuit 2.
522~1611KHz, 972~ with voltage controlled oscillator 11
There is a frequency change of 2 to 3 times 2061KHz, and since the frequency is relatively low, it is necessary to use a capacitor with a large capacitance change ratio and capacitance value, which has the disadvantage of increasing the price. It was hot.

Furthermore, once the assembly of the receiver is completed, in order to align the frequencies of the antenna circuit 1, high-frequency amplifier circuit 2, and voltage-controlled oscillator 11, there is no need to perform so-called tracking adjustment, in which coils, trimmer capacitors, etc. are adjusted. It had to be done.

The present invention eliminates the various drawbacks mentioned above, and
A new AM that can be applied to destinations with different channel spaces of 9KHz and 10KHz.
It provides a radio receiver.

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

FIG. 2 is a block diagram showing an embodiment of an AM radio receiver according to the present invention, in which circuits that are the same as those of the conventional system are given the same numbers.

In the figure, 13 is an antenna circuit, 14 is a high frequency amplification circuit, 15 is a first mixing circuit, 16 is a first intermediate frequency amplification circuit, 17 is a second mixing circuit, 18 is a second intermediate frequency amplification circuit, and the antenna circuit At least one of the high-frequency amplifier circuit 13 and the high-frequency amplifier circuit 14 includes a bandpass filter whose pass band is approximately the broadcast band, but unlike the conventional example, there is no tuning circuit and therefore no varactor diode. In addition, the first mixing circuit 15 mixes the broadband amplified signal via the high frequency amplifier circuit 14 with the oscillation signal f _L of the voltage controlled oscillator 11 in the phase-locked loop to generate the first signal.
An intermediate frequency f _IF1 is obtained, and the second mixing circuit 17 mixes the first intermediate frequency signal and the reference signal f ₀ to obtain a second intermediate frequency f _IF2 .

In the radio receiver of the present invention, the first intermediate frequency f _IF1 has a frequency sufficiently higher than the broadcast band to prevent image interference, and is often used in FM receivers, and filters can be obtained at low cost.
It is around 10.7MHz, and the channel space is specified to be 10.71MHz, which is a common multiple of 9KHz and 10KHz. That is, the oscillation frequency f _L of the phase-locked loop voltage controlled oscillator 11 is selected to be the sum or difference between the broadcast frequency to be tuned and the first intermediate frequency of 10.71 MHz.

Also, the second intermediate frequency f _IF2 is the channel space
It is a common multiple of 9KHz and 10KHz, and is specified at 450KHz, which is commonly used in the past from the viewpoint of selectivity, and the reference signal f ₀ has a channel space of 9KHz and 10KHz that can be supplied to the phase comparator 9, and , the first intermediate frequency is 10.71MHz, and the second intermediate frequency is
11.16MHz or 10.26MHz that can be mixed and converted to 450KHz
has been selected.

Therefore, in order to receive broadcast signals of 522KHz to 1611KHz, the oscillation frequency f _L of the voltage controlled oscillator 11 is
11.232MHz to 12.321MHz, the broadcast signal first passes through the antenna circuit 13 and/or the high frequency amplifier circuit 1.
The out-of-band signal is cut off by the band pass filter No. 4 and guided to the first mixing circuit 15, for example, 522K.
When receiving a Hz broadcast signal, the voltage controlled oscillator 11 oscillates at 11.232MHz, so 11.232−0.522
= 10.71MHz, and the first intermediate frequency is obtained.
Here, in the conventional example, without a tuning circuit, 522K
Hz and an image frequency of 1422KHz were received, but in the present invention, the image frequency is 11.232+
10.71=21.942MHz, and is sufficiently cut off by the bandpass filter of the antenna circuit 13 and/or the high frequency amplification circuit 14, so there is no need to worry about receiving the image frequency.

The first intermediate frequency of 10.71 MHz is amplified by the first intermediate frequency amplification circuit 16, and then mixed with the reference signal _f0 of 11.16 MHz or 10.26 MHz from the reference signal generation circuit 6 by the second mixing circuit 17, 450K
The second intermediate frequency f _IF2 is Hz.

The image frequency is 21.942MHz when receiving a 522KHz broadcast signal, but the image frequency is 522KHz to 1611K.
When receiving Hz broadcast signals, all image frequencies are 20MHz or higher, so there will be no image interference.

As described above, the AM radio receiver according to the present invention can prevent image disturbance without requiring a tuning circuit in the antenna circuit and the high frequency amplification circuit, and therefore, only one varactor diode is required in the voltage controlled oscillator. And this varactor diode is
The oscillation frequency of the voltage controlled oscillator is 11.232~12.321M
Since the frequency is high, Hz or 10.188 to 9.099MHz, and the change ratio is about 10%, a low-cost product with a small capacitance change ratio and a small capacitance value is sufficient. Furthermore, the first intermediate frequency is selected near the intermediate frequency of 10.7 MHz in FM receivers, and the second intermediate frequency is also selected to be 450 KHz, which is commonly used in AM receivers. Low-cost filters can be used in amplifier circuits.

In addition, since there is no tuning circuit in the antenna circuit and high-frequency amplification circuit, adjustments after the set is completed only need to check the variable range of the voltage controlled oscillator, which eliminates the large adjustment process of conventional tracking adjustment and improves the set yield. In addition, since no varactor diode is used in the receiving signal system, the disadvantages peculiar to varactor diodes such as distortion caused by large input signals can be eliminated, and the characteristics are improved. improves.

Furthermore, the first intermediate frequency, second intermediate frequency, and reference signal frequency are all selected to be a common multiple of 9KHz and 10KHz, so even if the channel space is 9KHz as in Japan or Europe, it will not be the same as in the United States.
Even at 10KHz, it can be applied to different destinations.

As described above, according to the present invention, by reducing the number of used parts, using low-priced parts, and reducing adjustment man-hours,
It becomes possible to realize an AM radio receiver with good characteristics and high productivity at a low price.

As the reference signal, the oscillation signal of the crystal oscillator may be used as is, or in some cases,
A frequency divider or a multiplier may be used to obtain the reference signal. Generally, a radio receiver can be configured without a high-frequency amplification circuit, and therefore, in the present invention, an antenna circuit having a bandpass filter whose pass band is approximately the broadcast band is used to transmit high-frequency signals. It is also possible to configure the device without the amplifier circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional AM radio receiver, and FIG. 2 is a block diagram showing an embodiment of the AM radio receiver according to the present invention. Explanation of main drawing numbers, 1, 13... antenna circuit,
2, 14...High frequency amplification circuit, 3...Mixing circuit,
4... Intermediate frequency amplification circuit, 5... Detection and low frequency amplification circuit, 6... Reference signal generation circuit, 7... Reference divider, 8... Programmable divider, 9... Phase comparator, 10... ...Low pass filter, 11...Voltage controlled oscillator, 12...Varactor diode, 15...First mixing circuit, 16...
...first intermediate frequency amplification circuit, 17...second mixing circuit, 18...second intermediate frequency amplification circuit.

Claims (1)

[Claims] 1. A reference divider that frequency divides a reference signal, a voltage controlled oscillator including a variable capacitance element, a programmable divider that frequency divides the output signal of the voltage controlled oscillator, a phase comparator that detects the phase difference between the two dividers, and A radio receiver having a phase-locked loop configured with a low-pass filter that integrates an output signal of a phase comparator and supplies a control voltage to the voltage-controlled oscillator, the radio receiver having a frequency higher than the broadcast band and a channel step of 9K.
The first intermediate frequency is a common multiple of Hz and 10KHz
The oscillation frequency of the voltage controlled oscillator is selected as the sum or difference between 10.71 MHz and the desired reception frequency, and is mixed with the broadcast signal obtained through a bandpass filter whose pass band is approximately the broadcast band, so that the center frequency is
a second mixing circuit for supplying the output signal of the voltage controlled oscillator to a first mixing circuit for obtaining a first intermediate frequency of 10.71 MHz, and for converting the first intermediate frequency to a second intermediate frequency of 450 KHz; The AM radio receiver is characterized in that the reference signal is supplied to the receiver, and the reference signal is set to a frequency that is the sum or difference of the first intermediate frequency and the second intermediate frequency.