JPH0621842A - Am electronic synchronization tuner - Google Patents

Abstract

PURPOSE:To allow the up-conversion system AM electronic synchronization tuner to receive selectively an MW band and an SW band without disturbance. CONSTITUTION:A signal inputted from an antenna is inputted to a tuning use lowpass filter section via a signal amplifier FET and an AGC transistor (TR). The tuning use low pass filter section consists of an MW use low pass filter 3 and an SW low pass filter 4 connected in parallel and a bias changeover circuit 6 selects either of them. The selected low pass filter circuit receives one of the MW and SW bands and outputs the signal of the band to an IC 5 forming the up-conversion system frequency conversion section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an up conversion type AM electronic tuning tuner for selecting a signal in a predetermined band by a low pass filter.

[0002]

2. Description of the Related Art Conventional up-conversion AM
As shown in FIG. 2, the electronic tuning tuner includes a signal amplification FET 1 for amplifying a signal input from an antenna, an AGC transistor 2 for AGC controlling an RF signal output from the signal amplification FET 1, and an AGC transistor 2. The low pass filter 3 receives as an input the output of 1) and selects and outputs a signal in a predetermined band, and the IC 5 which constitutes an up-conversion frequency converter having the output of the low pass filter as an input. L1 and L2 are resonance coils, C1, C2 and C3 are resonance capacitors, C4 is a coupling capacitor, L3 is a Vcc filter coil, and R1 is a bias resistor.

The above-mentioned AM electronic tuning tuner receives the MW band by using, for example, a 3.9 Mz low-pass filter as the low-pass filter 3.
It prevented the interference of the signal of 3.9 Mz or more.

[0004]

However, the conventional AM electronic tuning tuner is exclusively for MW, and if a low-pass filter having a large cutoff frequency is used to extend the reception band to receive signals up to the SW band, the disturbance will occur at night. There was a problem that was greatly affected. It is an object of the present invention to solve the above problems and provide an AM electronic tuning tuner capable of selectively receiving the MW band and the SW band without interference.

[0005]

SUMMARY OF THE INVENTION The present invention provides an AM electronic tuning tuner for high-frequency amplifying a signal input from an antenna with an RF amplifier circuit, selecting a signal in a predetermined band from the amplified signal, and performing frequency conversion. A circuit provided with a parallel connection circuit of a low pass filter circuit for MW and a low pass filter circuit for SW, which receives the output of the RF amplification circuit, and a bias switching circuit for selectively switching the biases of the low pass filter circuits. Is.

[0006]

According to the present invention, the MW is changed by the bias switching circuit.
By selectively switching the external bias of the low pass filter for SW and the low pass filter for SW, the enable state is selectively established.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 1 is a circuit diagram showing an embodiment of an AM electronic tuning tuner according to the present invention. In FIG. 1, 1 is a signal amplification FET for amplifying a signal input from an antenna, and 2 is an output from a signal amplification FET 1. AGC transistor for AGC controlling the RF signal, 3 is input to the output of the AGC transistor, 3.9 Mz low pass filter for MW 3, 4 is 18 Mz connected in parallel with MW low pass 3
SW low-pass filter, 5 is an IC that constitutes a frequency conversion unit that receives the outputs of the MW low-pass filter 3 and the SW low-pass filter 4, and 6 is two in the MW low-pass filter 3 and the SW low-pass filter 4. A bias switching circuit for selectively supplying the external biases MWVcc and SWVcc, L1, L2, L4, and L5 are resonance coils, C1 to C6 are resonance capacitors, C7 is a coupling capacitor, L3 and L6 are Vcc filter coils, and R1. , R
Reference numeral 2 is a bias resistor, R3 is a counter resistor, and D1 to D4 are RF switch diodes.

Next, the operation of the AM electronic tuning tuner thus constructed will be described. The signal input from the antenna is subjected to high frequency amplification by the signal amplification FET 1, and then is controlled to a constant level by the AGC transistor 2 and output to the low pass filter section. The bias switching circuit 6 is included in the MW filter 3 of 3.9 Mz and the SW filter 4 of 18 Mz.
Bias MWVcc and SWVcc are selectively applied, and one of the MW band and the SW band is selectively received from the RF signal output from the AGC transistor 2 by the switching operation of the RF switch diodes D1 and D2. One of the signals in the selected MW band and SW band is supplied with the RF switch diodes D3 and D in the ON state.
It is input to the IC 5 which constitutes the frequency conversion unit of the up-conversion system via 4.

In the IC5 which constitutes the frequency conversion unit, the first
Since the intermediate frequency is set to 10.7 Mz, the first local oscillation frequency is set to “desired frequency + 10.7 Mz” by the first mixer.
The input signal is selected as, and the signal converted to 10.7 Mz is input to the second mixer through the 10.7 Mz filter. In the second mixer, the second local oscillation frequency is set to 10.25 in order to obtain the selectivity with the filter of 450 kHz.
Convert to a second intermediate frequency of 450 kHz as Mz.
After that, in the output stage circuit, amplification and detection are performed and output as an audio signal.

In the above-described embodiment, by providing the bias of the low-pass filter on the band side desired to be received among the two low-pass filters, it can be used as a tuner for both MW and SW.

The circuit configuration of the low-pass filter and the bias method are not limited to those in the above embodiment.

[0012]

As described above, according to the present invention, the AM electronic tuning tuner of the up-conversion system can receive up to the SW band, and at the time of receiving the MW band, the interference of the SW band signal or the like is prevented. Has the effect of not receiving.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an AM electronic tuning tuner according to the present invention.

FIG. 2 is a circuit diagram of a conventional AM electronic tuning tuner.

[Explanation of symbols]

 1 FET for signal amplification 2 AGC transistor 3 MW low-pass filter 4 SW low-pass filter 5 IC 6 Bias switching circuit

Claims (1)

[Claims] 1. An AM electronic tuning tuner that performs high frequency amplification of a signal input from an antenna by an RF amplification circuit, selects a signal in a predetermined band from the amplified signal and performs frequency conversion, and inputs the output of the RF amplification circuit. An electronic tuning tuner characterized by comprising a parallel connection circuit of a low pass filter circuit for MW and a low pass filter circuit for SW, and a bias switching circuit for selectively switching the biases of the low pass filter circuits.