JPH01176121A - Fm reception circuit - Google Patents

Abstract

PURPOSE:To improve the quality of electric field information of a broadcast station by selecting a frequency of an output of a voltage controlled oscillator as twice the IF frequency, applying 1/2 frequency division, giving the result to a phase comparator in the state of locking an output of a voltage controlled oscillator and giving a frequency signal of the voltage controlled oscillator to a synchronous detector via an inverter and a 1/2 frequency divider. CONSTITUTION:A phase comparator 6, a low pass filter 7, a voltage controlled oscillator(VCO) 7, and a 1/2 frequency divider 9 form a PLL detector. The oscillating frequency of the VCO 7 is doubled to a frequency of the IF signal at locking. Since the synchronizing input signal of the synchronous detector 12 is synchronous with the IF signal by an inverter 10 and a 1/2 frequency divider 11 and the detected IF signal is a signal extracted from a mixer output, the detected output has a linearity with respect to the antenna input signal. Thus, the quality of the electric field information of a broadcast station is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an FM receiver, and more particularly to a signal meter circuit.

[Conventional technology]

Conventionally, this type of signal meter circuit detects the level of a multistage IF signal amplification circuit that amplifies the IF signal output from the frequency conversion circuit (mixer circuit) of the FM receiver, and then detects the level of the multistage IF signal amplification circuit that amplifies the IF signal output from the frequency conversion circuit (mixer circuit) of the FM receiver. Add the signals and
It is used as a signal meter output.

[Problem that the invention seeks to solve]

The conventional signal meter circuit described above has each
Since the signal amplification circuit is a limiter amplifier to stably receive the FM signal, the detected signal also has the characteristics of a limiter, and the detected signal is further added to become the signal meter output. , as shown in FIG. 3, has the disadvantage that it is not linear with respect to the input signal.

[Means for solving problems]

The signal meter circuit of the present invention includes a phase comparator to which an IF ratio output is applied to one input, and a voltage controlled oscillator to which the output of the phase comparator is applied via a low-pass filter,
It has a PLL detector which adds the oscillation output of the voltage controlled oscillator to the other input of the phase comparator and takes out the FM detected audio signal to the output of the low pass filter, and when the output of the voltage controlled oscillator is locked, the IF frequency is The frequency signal of the voltage controlled oscillator is doubled and input to the input of the phase comparator by dividing the frequency by 1/2, and the frequency signal of the voltage controlled oscillator is sent to the synchronous detector via the inverter and the 1/2 frequency divider. The IF multiplied signal of the mixer circuit output for frequency conversion is detected.

〔Example〕

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

FIG. 1 is a block diagram of one embodiment of the present invention.

The radio waves received by the antenna 1 are amplified by a high frequency amplifier circuit 2, frequency-converted by a mixer circuit 4 based on the signal from a local oscillation circuit 3, and the IF-multiplied signal is amplified by an IF-multiplied signal by an IF amplification circuit 5 and a phase comparator 6. becomes the input. Phase comparator 6, low pass filter 7, voltage controlled oscillator (VCO) 7
．． The 1/2 frequency divider 9 forms a PLL detector. VCO7
The oscillation frequency of is twice that of the IF signal when locked.

10 is an inverter, 11 is a 172 frequency divider, and the synchronized input signal of the synchronous detection 12 is synchronized with the IF multiplied signal, and the signal is taken out from the detected IF multiplied signal mixer output, as shown in Figure 3. In addition, the detection output has linearity with respect to the antenna input signal. Note that 13 is a low-pass filter that lowers the frequency of the signal meter output.

FIG. 2 is a block diagram of another embodiment of the invention. 1st
The difference from the diagram is that between the mixer output and the synchronous detection input,
A filter 15 for band limiting is inserted. In this block diagram, since band-limited synchronous detection is used, there is an advantage that if there is a signal from an adjacent station, the signal information of the adjacent station is difficult to enter into the signal meter output.

〔Effect of the invention〕

As explained above, in the present invention, since the signal meter output has linearity with respect to the antenna input signal, the quality of the electric field information of the broadcasting station is improved. It becomes easy to compare the ranking of strength, and the microcomputer control of the receiver allows
This has the effect of making it easier to rank receiving broadcast stations.

It is also possible to widen the band of the 13 low-pass filters and extract the IF multiplied signal AM component, and the IF multiplied signal A
Since the M component is multipath information and external noise information,
Good linearity of detection means that the quality of the information is also good.

[Brief explanation of the drawing]

FIGS. 1 and 2 are block diagrams showing embodiments of the present invention, and FIG. 3 is a signal meter output diagram according to the present invention. 1...Antenna, 2...High frequency amplification circuit, 3...Local oscillation circuit, 4...Mixer circuit, 5...IF amplification circuit, 6...
・Phase comparator, 7...Low pass filter,
...Voltage controlled oscillator, 9, 11...1/2
Frequency divider, 10... Inverter, 12...
・Phase detector, 13...Low pass filter, 1
4...Audio amplifier, 15...Band filter. Agent: Patent Attorney Susumu Uchihara, $l Closed $2

Claims (1)

[Claims] A phase comparator to which an IF output is applied to one input, and a voltage controlled oscillator to which the output of the phase comparator is applied via a low-pass filter, and the oscillation output of the voltage controlled oscillator is applied to the other input of the phase comparator. PLL which extracts the FM detected audio signal to the output of the low pass filter in addition to the input of the
In an FM receiving circuit having a wave detector, the output of the voltage controlled oscillator is made to have a frequency twice the IF frequency when locked, and the frequency is divided into 1/2 and inputted to the input of the phase comparator, and the frequency signal of the voltage controlled oscillator is inputted to the input of the phase comparator. is sent to a synchronous detector via an inverter and a 1/2 frequency divider, and the input of the synchronous detection is detected as an IF signal of the mixer circuit output for frequency conversion, and this detected signal is sent to the signal meter output, which is electric field strength information. An FM receiving circuit characterized by: