JPS60223335A - Turner of am/fm receiver - Google Patents

Abstract

PURPOSE:To decrease the number of externally mounted components to an IC without any clock signal generating circuit especially by constituting an intermediate frequency transformer of an AM receiver with a switched capacitor filter and obtaining a clock signal driving the switched capacitor filter from a frequency signal of a PLL synthesizer. CONSTITUTION:A mixing circuit 23 mixes frequencies of a reception signal fo and a local signal fL and applies an intermediate frequency signal If of 455kHz in frequency to a band pass filter 25. The band pass filter 25 consists of a switched capacitor filter (SCF). Then clock signals phi, phi' of the SCF acting as the band pass filter 25 are obtained without any special generating means. That is, a reference frequency signal fref is fed to a frequency divider 26 and a prescaler 30 via a line l1. A frequency divider 26 and an inverter 27 applies frequency division to the reference frequency signal fref to obtain the clock signals phi, phi'. It is desirable that the frequency of the clock signals phi, phi' is in the relation of phi>455kHzX2, because the center frequency of the intermediate frequency signal is 455kHz and the frequency divider 26 is set to the frequency dividing ratio to satisfy this condition.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to an AM/FM receiver team.

[Background technology]

In the AM receiver, a bandpass filter with a center frequency of 455 KH2 is used in the intermediate frequency amplification circuit. This is the black first-come-first-served F, first published on April 10, 1978.
As shown in the M Tuner Manual, Radio Technology Co., Ltd., the purpose is to reduce noise in AM receivers.

This bandpass filter is composed of a resonant circuit of a coil and a capacitor.

On the other hand, not only AM receivers but also various electronic devices tend to be integrated into semiconductor integrated circuits. The present inventor conducted various technical studies on the AM receiver from such a technical viewpoint.

As a result, it has been revealed that the coils and capacitors constituting the bandpass filter must be external components, which increases component costs and wiring man-hours, contributing to higher costs. It has also been revealed that the IC must be provided with an external connection terminal for a bandpass filter, which reduces the degree of integration.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a receiver that utilizes a Swiss-isotide capacitor filter instead of a bandpass filter using a coil and a capacitor, thereby reducing the number of external components such as a coil and a capacitor.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief summary of the invention disclosed in this application is as follows:
It is as follows.

That is, in the AM/FM receiver team, AM
The receiver's intermediate frequency transformer is a switched capacitor.
The present invention comprises a filter, and obtains a clock signal from a frequency signal of a PLL synthesizer, which is a clock signal for driving the switched e-capacitor filter, without particularly providing a clock signal generation circuit, and furthermore, reduces the number of external parts of an IC. The goal is to achieve the following objectives.

〔Example〕

Hereinafter, with reference to FIGS. 1 to 3, A to which the present invention is applied
An example of an M/FM receiver will be described. In addition, Figure 1 is A
This shows the overall circuit configuration of the M/FM receiver, and although not particularly shown, it is assumed that it is implemented as a semiconductor integrated circuit.

First, the FM receiver shown in the upper part of FIG. 4 will be described, and its circuit configuration and circuit operation are known to those skilled in the art. Therefore, an outline of the circuit operation of the FM receiver will be described. 1 is a receiving antenna, 2 is a high frequency amplification circuit (hereinafter referred to as an RF circuit), and a received signal fo selected by the RF circuit 2 is supplied to a mixing circuit 3. The mixing circuit 3 receives the received signal f. frequency mixing with the local signal fL supplied from the local oscillation circuit 4 is performed. An intermediate frequency signal Xf with a center frequency of 10.7 MH2 is obtained from the mixing circuit 3 and is supplied to the intermediate frequency circuit 5.

The output signal f' of the intermediate frequency circuit 5 is supplied to an FM detector 6, from which a detected output VD is obtained. Detection output■. is supplied to the FM demodulator 7 to obtain demodulated L and R signals.

Next, the circuit operation of the PLL synthesizer will be explained.

The reference frequency signal generator 11 has a crystal oscillator and generates an extremely stable reference frequency signal fref.

The reference frequency signal 'ref is the grease scaler 1 on the FM side.
2 and is also supplied to the AM side, but the F
The circuit operation will be explained sequentially starting from the M side.

The prescaler 12 receives a reference frequency signal fref, and the local oscillation circuit 4 receives a frequency signal f. sc is generated and executed. A frequency signal f0 corresponding to the phase difference obtained from the programmable divider 15 is supplied to the low-pass filter 16,
A control voltage vc is obtained from the low-pass filter 16 and supplied to the local oscillation circuit 4. The local oscillation circuit 4 is a voltage controlled oscillation circuit having a voltage controlled capacitance element, and has a control voltage V.
The capacitance of the capacitive element is varied by changing the voltage level of C, which changes the frequency of the local signal fL and also the frequency signal f. 8o is controlled. f from the frequency signal. s
c ``N'''ref, determined by the programmable divider-50 frequency division ratio N.

Next, the AM receiver shown in the lower part of FIG. 1 will be explained.

21 is a receiving antenna, 22 is an RF circuit, 23 is a mixing circuit, and 24 is a local oscillation circuit. The received signal f selected from the RF circuit 22 to the mixing circuit 23.

is supplied, and further a local signal f is supplied from the local oscillation circuit 24.
L is supplied. The mixing circuit 2 performs frequency mixing of the received signal fo and the local signal fL, and outputs a frequency of 455 KH.
The intermediate frequency signal If of No. 2 is supplied to the bandpass filter 25.

The bandpass filter 25 is constituted by a switched cabactor filter (hereinafter referred to as SCF), and an example of its circuit configuration is illustrated in FIGS. 2 and 3. The SCF uses capacitors, but each capacitor is a capacitor formed within the IC rather than being connected outside the IC. Therefore, the bandpass filter 25 does not require a coil or an external capacitor, and can be formed within the IC.

What should be noted is that the clock signal φ,7 of the SCF operating as the bandpass filter 25 can be obtained without providing any special generating means.

That is, the reference frequency signal fref is on the line t1.
The signal is supplied to the frequency divider 26 and the grease scaler 30 via the frequency divider 26 and the grease scaler 30. In relation to the SCF, the frequency divider 26 and the inverter 27 are provided to frequency-divide the reference frequency signal fref and obtain clock signals φ and φ. Since the center frequency of the intermediate frequency signal is 455 KHz, the frequency of the clock signals φ, φ is preferably φ)455KHX2, and the frequency divider 26 is set to a frequency division ratio that satisfies this condition.

By passing the intermediate frequency signal If through the bandpass filter 26, an output signal If' from which noise components have been removed is supplied to the intermediate frequency circuit 28. Removal of the noise component makes it possible to remove so-called inter-office noise (noise generated in a no-signal band between a desired broadcast frequency and another broadcast frequency).

The output signal If' of the intermediate frequency circuit 28 is supplied to an AM detector p29, from which a detected output VD, that is, an audio signal is obtained.

Next, the PLL synthesizer in the AM receiver will be explained.

Prescaler 30 supplies a reference frequency signal fref. On the other hand, the programmable divider 32 is supplied with the frequency signal fA from the local oscillation circuit 24 to the output 31 .

A phase comparison is performed with respect to the frequency signal, and an output signal corresponding to the phase difference between the two is supplied to the low-pass filter 33. The local oscillation circuit 24 is controlled by the control voltage vc obtained from the low-pass filter 33, and the local signal fL2
The frequency signal fA is stabilized based on the reference frequency signal fref.

Next, a specific example of the bandpass filter 25 will be described.

Note that the bandpass filters using SCFs shown in FIGS. 2 and 3 are all well known.

The bandpass filter shown in FIG. 2(g) is called a second-order SC bandpass filter.

The capacitor C1 is for direct current blocking, and the first operational amplifier 41 and the capacitor C that transmits signals by charging and discharging.
2, C8, C6, switch S3.

A bypass filter HPF is configured by S4.

Also, a second operational amplifier 42, capacitors C4 and C6 that transmit signals by charging and discharging, switches S, , S2
constitutes a low-pass filter LPF. switch 811
S2. S3+s4 is driven by the clock signals φ and φ from the switching state shown by the solid line to the switching state shown by the dotted line. By driving the switches S and ~S4, the output signal of the bypass fill HPF is passed through the low-pass filter L.
It will be supplied to PF. By combining these two frequency characteristics, an output gain characteristic as shown in ) in FIG. 2 is obtained.

Moreover, the bandpass filter shown in FIG. 3(4) has a first
operational amplifier 43, and a capacitor CI2. which transmits signals by charging and discharging. C10, a bypass filter HPF composed of switches Sll+sty; a second operational amplifier 44; a low-pass filter LPF composed of capacitors C,4,C,,,C,, switches SI3+S14, which transmit signals by charging and discharging; It consists of. Since the output signal of the bypass filter HPF is supplied to the low-pass filter LPF, the output signal V. ut has an output gain characteristic as shown in FIG. 30.

The bandpass filters shown in FIG. 2(c) and FIG. 3(5) both have band-pass characteristics as shown in FIG. 2(c) and FIG. 3(0), so the bandpass filters shown in FIG. Available for 25 days.

Each capacitor used in the bandpass filter is
It can be formed within the IC, and the clock signal φ
, φ can also be obtained from within the same IC, so the number of external parts can be significantly reduced.

〔effect〕

(1) The intermediate frequency transformer that was installed as an external part in the receiver IC can be removed, and instead, a bandpass filter made of SCF can be installed inside the IC, so the external parts can be replaced. This has the effect of reducing

(2) Since the clock signal for driving the SCF can be obtained from a reference frequency signal provided for another purpose, there is no need to provide a particular clock signal generation circuit, and the circuit configuration can be simple.

[Application field]

In the above description, the invention made by the present inventor has been mainly applied to an AM receiver, which is the field of application in which the invention is based, but the invention is not limited thereto.

For example, it can be used in a television receiver.

Also, if it has an AM or FM receiver, it can be used as a car radio.

It can be used regardless of the type of Votaple radio.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an AM/FM receiver to which the present invention is applied, FIG. 2 (5) is a circuit diagram showing a first example of a bandpass filter, and FIG. FIG. 3(5) is a circuit diagram showing a second example of a bandpass filter. FIG. 30 is a frequency characteristic diagram of the bandpass filter. DESCRIPTION OF SYMBOLS 11... Reference frequency signal oscillation circuit, 25... Band pass filter, 26... Frequency divider, 27... Inverter, φ, φ... Clock signal.

Claims (1)

[Claims] 1. In the tuner of the AM/FM receiver, the bandpass filter of the AM intermediate frequency circuit is configured with a switched capacitor filter, and the switched capacitor filter
1. A tuner for an AM/FM receiver, characterized in that it is configured to be based on an output signal of a reference frequency oscillator of a PLL synthesizer, which is a clock signal for driving a filter.