JPS58177036A - Am radio receiver - Google Patents

Abstract

PURPOSE:To save the number of components and adjusting manhours and to simplify the constitution of an AM receiver for demands of different channel frequencies, by selecting the oscillating frequency from a VCO supplied to the 1st and the 2nd mixing circuits for the forming of the 1st and the 2nd IF signals. CONSTITUTION:A PLL circuit of the AM receiver consists of the VCO11 using a varactor diode 12, a programmable divider 7, a reference signal generator 6, a phase comparator 9, and an LPF10. The oscillating frequency of the VCO11 of the PLL circuit is selected to the sum or subtraction of a desired reception frequency and the 1st IF of 10.7MHz frequency. The output signal from the VCO11 is supplied to the 1st mixing circuit 15, where the signal is mixed with a broadcast signal corresponding to the broadcast band passing through a high frequency amplifier 14 and the 1st IF signal is outputted. Further, the reference signal from the circuit 6 is added to the 2nd mixing circuit 17, where the signal is mixed with the 1st IF signal and the 2nd IF signal of 450kHz frequency is outputted. Thus, the number of components and the manpower for adjustment are saved.

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 frequency P-de has 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), a reference signal generation circuit using a crystal oscillator (6), a reference divider (7), a programmable divider (8),
It consists of a phase comparator (9), a low-pass filter Q□, and a voltage-controlled oscillator Qll as a local oscillator, and the antenna circuit (1) and seven high-frequency/amplification circuits (2) are tuned including four varactor diodes, which are variable capacitance elements. The circuit had a father, voltage controlled oscillator on which also contained four buffed diodes.

Then, each of the antenna circuit (1), the high frequency amplifier circuit (2), and the voltage controlled oscillator 1111 has a back-to-back diode □
Supply the control voltage from the low-pass filter QO to Doro,
Broadcast signals were received by supplying the output signal of the voltage controlled oscillator 011 to the mixing circuit (3).

Therefore, if the broadcast band is 522-1611 KHz and the channel space is 9 KHz, for example, 5
In order to receive a 22 KHz broadcast signal, if the intermediate frequency is 450 KHz, the oscillation frequency of the voltage controlled oscillator all should be set to 522+450=972 KHz.

However, broadcast signals usually pass through a tuning circuit consisting of an antenna circuit (1) and a high frequency amplification circuit (2) before being sent to a mixing circuit (3).
However, if there is no tuning circuit, 522KH
Even if the oscillation frequency of the voltage controlled oscillator an is set to 972 KHz in an attempt to receive the broadcast signal of z, the broadcast signal of the image frequency of 972+450=1422 KHz will also be received. Therefore, the 522KHz you are trying to receive
In order to guide only nearby frequencies to the mixing circuit (3), the conventional antenna circuit (1) and high frequency amplifier circuit (2) are used.
) required a tuned circuit.

However, the resonant frequency of the coaxial circuit had to be changed depending on the receiving frequency, and for this reason a varactor diode (2) was required in each tuned circuit. Rabbit,
In conventional radio receivers, the varactor diode is always 8s.
It was needed there. Moreover, the oscillation frequency of the voltage controlled oscillator nt+, the antenna circuit (1) and the high frequency amplifier circuit (2)
) must change in conjunction with each other, and in order to reduce the tracking effect, each varactor diode must have the same characteristics. Furthermore, the variable range of the varactor diode is limited to the antenna circuit (1) and the high frequency amplification circuit w! ? (2)
522-1611KHz, voltage controlled oscillator q℃ 97
There is a frequency change of 2 to 8 times, from 2 to 2061 KHz,
In addition, since the frequency is relatively low, a capacitance change ratio and a capacitance value must be large, resulting in a high price.

Also, when the receiver assembly is completed, the antenna circuit (1), high frequency amplifier circuit (2) and voltage controlled oscillator Ov
In order to align each frequency, it was necessary to perform so-called tracking adjustment, which involves adjusting the coils, trimmer capacitors, etc.

The present invention provides a new AM radio receiver which eliminates the various drawbacks mentioned above and which can be applied to different destinations with channel spacings of 9 KHz and 10 KH2.

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 prior art are given the same numbers.

In the figure, day is the antenna circuit, Q41 is the high frequency amplification [circuit,
αθ is the first mixing circuit, 00 is the first intermediate frequency amplification circuit, α
The second mixing circuit 081 is a second intermediate frequency amplification circuit, and at least one of the antenna circuit port and the high frequency amplification circuit 0 has a bandpass filter whose pass band is approximately the broadcast band. In contrast, it does not have a tuning circuit and therefore does not have a varactor diode. Also, the first
The mixing circuit αe mixes the wideband amplified signal via the high-frequency amplifier circuit α station with the oscillation signal fL of the voltage-controlled oscillator Qn in the phase-locked V-wave, and generates the first intermediate frequency f.
lF1 is obtained, and the first intermediate frequency signal and the reference signal fO are mixed in the second mixing circuit αη to obtain the second intermediate frequency @flF2.

In the radio receiver of the present invention, the first intermediate frequency f
■The frequency of y1 is sufficiently high compared to the broadcast band to prevent image interference, and it is around 10.7MHz, which is often used in FM receivers and filters can be obtained at low cost, and the channel spacing is 9KHz and 10KHz.
10.71 MHz, which is a common multiple of . That is, the oscillation frequency fL of the voltage controlled oscillator q°C of the phase locked loop 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 fxy2 has a channel space of 9K.
It is a common multiple of Hz and 10KHz, and is specified at 450KHz, which is commonly used from the viewpoint of selectivity.
And, the standard signal Ji+fo is channel space 9K
Hz and 10KHz can be supplied to the phase comparator (9), and the first intermediate frequency 1071MHz can be supplied to the second intermediate frequency 45MHz.
11.16MHz or 10 that can be mixed and converted to 0'KHz
．． 26MHz is selected.

Therefore, in order to receive the W transmission signal of 522 KHz to 1611 KHz, the oscillation frequency fL of the voltage controlled oscillator qll is
If it is 11.282MHz-12,821MHz,
The broadcast signal is first cut out of the band by the band pass filter of the antenna circuit and/or the high frequency amplifier circuit 04, and then guided to the @1 mixing circuit α9. For example, when receiving a 522 KHz broadcast signal, the voltage controlled oscillator 1ull is Since it oscillates at 11.2B2MHz, 11.282-0
．． 522=10.71 MHz, and the first intermediate frequency is obtained. Here, in the conventional example, without the same circuit, 5
1 422KH which is the image frequency along with 22KHz
7 was received, but in the present invention, the image frequency is 11
, 282 + IO, 71 = 21.9 - 2 MHz, and is sufficiently cut by the band pass filter on the antenna circuit a3 and/or the high frequency amplifier circuit side, so there is no need to worry about receiving the image frequency.

Then, the first intermediate frequency of 10.71 MHz is amplified by the first intermediate frequency amplification circuit (to), and then 11.16 MHz or 10.26 MHz from the basic TS signal generation circuit (6)
Standard belief JP! It is mixed and converted in the rfO and fa2 mixing circuit node, resulting in a second intermediate frequency flP2 of 450 KHz.

The image frequency is 21.942MHz when receiving a 522KHz broadcast signal, but
When receiving a 611 KHz broadcast signal, all image frequencies are 20 MHz 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. The oscillation frequency of the voltage controlled oscillator of this varactor diode is 11.
282~12.821MHz5 (FiIO, 188~9
．． Since the frequency is as high as 0.099 MHz and the change ratio is about 10%, a low-cost device with a small appearance change ratio and a small capacitance value is sufficient.

Furthermore, the first intermediate frequency is set to intermediate frequency 1 on the FM receiver.
0.7 MHz, and the second intermediate frequency is also selected to be 450 KHz, which has traditionally been commonly used in AM receivers, so each intermediate frequency amplification circuit can be used at a low cost) (
A/Meta-Can be used.

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 possible f range of the voltage-controlled oscillator, eliminating the large adjustment process of conventional tracking adjustment. It is possible to improve the node yield and greatly reduce the adjustment cost, and in terms of characteristics, since no varactor diode is used in the receiving signal thread, it eliminates the disadvantages peculiar to varactor diodes, such as the generation of cracks when receiving large power signals. and the characteristics are improved.

Furthermore, since the first intermediate frequency, second intermediate frequency, and reference signal frequency are all selected to be a common multiple of 9 KHz and 10 KHz, even if the channel space is 9 KHz as in Japan or Europe, it is similar to that in the United States. Even if it is 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 the number of adjustment steps, it becomes possible to create an AM radio receiver that is inexpensive, has good characteristics, and is highly productive.

Incidentally, as the reference signal, the oscillation signal of the crystal oscillator may be used as it is, or in some cases, a frequency divider or a multiplier may be used to obtain the reference signal. Furthermore, in general, it is possible to configure a radio receiver without a high-frequency amplification circuit, and therefore, in the present invention, an antenna circuit having a bandpass filter whose passband is approximately the broadcasting band is used. It is also possible to configure the device without the ll1 frequency amplification 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

Claims (1)

[Claims] (1) A reference divider that divides the frequency of a reference signal, a voltage controlled oscillator that includes a variable capacitance element, a programmable divider that divides the output signal of the voltage controlled oscillator, and a phase comparison that detects the phase difference between the two dividers. device, the phase ratio #
In a radio receiver having a phase-locked loop comprising a low-pass filter that integrates an output signal of an R unit and supplies a control voltage to the voltage-controlled oscillator, the oscillation frequency of the voltage-controlled oscillator is equal to the desired receiving frequency and 10.7
Through a Pandpass 4AI filter selected as the sum or difference from the first intermediate frequency of 1 MHz, and with the broadcast band as the approximate passband,
The center frequency is 10.7 when mixed with the broadcast signal obtained by
The output signal of the voltage controlled oscillator is supplied to a first mixing circuit for obtaining a first intermediate frequency of 1 MHz, and the reference signal is Ft.
AM radio receiver, characterized in that the AM radio receiver is configured to supply a second mixing circuit for converting the signal to a second intermediate frequency signal of z to a second intermediate frequency signal.