JPS62149226A - Fm receiver - Google Patents

Abstract

PURPOSE:To obtain an FM receiver capable of high sensitive reception while keeping high S/N and high selectivity by controlling FM feedback quantity in response to the level of the FM detection output. CONSTITUTION:The circuit has an FM negative feedback loop so as to decrease the frequency shift of the FM signal passing through an IF filter 3. Since the 1st VCA circuit 6 controlled by the output of a level detection circuit 7 is con nected, the feedback quantity of the FM negative feedback changes in response to the level of the FM detection output. In using the circuit 7 having a character istic shown in figure, when the detection output level is low, the detection output shown in a point A has nearly the same characteristic as that without any feedback shown in solid lines. The 2nd VCA circuit 9 is connected to the output of the FM detector 4 and controlled by a signal corresponding to the output of the circuit 7. Thus, the detection output of a point B is corrected to the original linear characteristic as shown in broken lines in figure.

Description

[Detailed Description of the Invention] [Field of application in confectionery] This invention relates to an FM receiver, in particular, high sensitivity, high selectivity,
High S/N should be obtained (F equipped with FM negative feedback means'fr)
This relates to the M receiver.

[Takumi rice technology]

FIG. 5 shows a block diagram of a conventional FM receiver that performs negative FM feedback. 51 is a high frequency amplification circuit, the output of which is connected to the frequency conversion circuit 2. In FIG. Frequency conversion circuit 2
The output of is connected to an FM# wave circuit 4 via a filter 3. The output of the FM detection circuit 4 is connected to a local oscillation circuit 5, and the output of the local oscillation circuit 5 is further connected to the frequency conversion circuit 2, thereby forming a so-called FMfjL feedback receiver.

Next, the operation will be explained.

Input signal Vi inputted from the antenna δ (amplified by the high frequency RI circuit 1 and converted to an intermediate frequency signal by the frequency conversion circuit 2. This intermediate frequency signal dFM! is FM detected by the countertalk 4, and its detection output is returned to the local oscillation circuit 5.

Does the local oscillation circuit 5 have an oscillation frequency depending on the human voltage? It is a controllable VCO (', if controlled oscillator) which is a detected output and whose oscillation frequency is controlled so that the frequency deviation of the intermediate frequency signal input to the filter 3 is small. Since the frequency deviation is reduced by the negative NI feedback, the band of the filter 3 can be narrowed.As a result, the threshold/hold level is lowered and a highly sensitive receiver can be realized.

[Problem that the invention seeks to solve]

However, the conventional technology has the following drawbacks.

In other words, since the frequency deviation is reduced by the FM negative feedback, the FM detection output becomes smaller and the S/N ratio deteriorates. Furthermore, if there is an interfering signal in the vicinity, the interfering signal is also compressed by negative feedback, making it difficult to obtain high selectivity even if a comfortable filter is used.

[Means for solving problems]

This invention was made in order to eliminate the drawbacks of Takumi's circuit, and was made with the level of FM detection output in mind.
By controlling the return foot, a s/N% a
[Embodiment of the Invention] FIG. 1 shows the factor A of the present invention.

In the figure, the high frequency stage 1 is a circuit 1, and its output is input to a frequency conversion circuit 2. Frequency variation time i
Il! The output of 2 is connected to the filter 3iC, and its output is input to the 5FM filter 4 which is input to the FM filter 41C. is connected, and the output of this level detection circuit 7 is connected to the mlj control terminal of the first VCA circuit 6.

The output ri of the first VCA circuit g6 is connected to the local oscillation circuit 5, and the output of the VCC local oscillation circuit 5 is further input to the frequency conversion circuit 1162, thereby forming an FM negative feedback loop.

Further, the output of the FM detection circuit 4 is supplied with a second VCA circuit, i! When r9 is connected, the output of the level adjustment circuit 8 connected to the output 1c of the level detection circuit 7 becomes I? I11 is under control.

Next, the operation of the present invention will be explained. The operation of the high frequency amplification first-order circuit 1, frequency conversion circuit 2, filter 3, FM detection circuit 4, and local oscillation circuit 5 is the same as the conventional example shown in FIG. 2, and the IF filter An FM negative feedback loop is configured to reduce the frequency deviation of the F'M signal passing through the FM signal. However, the first
Since the VCA circuit 6 is connected, the amount of FM negative feedback changes in accordance with the level of the FM detection output.

When using the level production circuit 7 having the characteristics shown in Figure 2, when the detection output level is low, l/( is the first V
Since the gain of the CAl path 6 is small and the amount of feedback is small, the detection output at point A in Fig. 1 has almost the same characteristics as when there is no feedback, as shown by the solid line in Fig. 3. , as the detection output level increases, the first V
The gay/ of the CA circuit 6 also increases, and mat
1#I is added, so the output at point A exhibits saturation characteristics as shown in Fig. It is controlled by a signal corresponding to the output of the circuit 7. As a result, the detection output at point B is corrected to the original linear characteristic as shown by the broken line in FIG.

In this way, the frequency deviation of the intermediate frequency signal passing through the filter 3 is compressed non-directly depending on the I/I ratio of the input signal, so it is recommended to use a narrow band filter for the filter 3. This improves the thread/hold level and improves sensitivity.

Also, even if there is an interfering signal nearby, the level of the FM detection output must exceed a certain level.
Since the M shell/feedback does not work, the narrow band filter operates as a narrow band and a sufficient selection variation can be obtained.

Further, if a level detection circuit having a non-responsive property is used as shown in FIG. 4, the level detection circuit will be even more resistant to interference signals. This is because when the detection output level is within this dead band, the amount of feedback is low and the receiver operates as a normal narrowband receiver.

Furthermore, when the modulation rate is low v'h, it is the same as a normal receiver, so there is no deterioration in S/N.

In addition, the above aSI! In the light, the FM test u4 (D output Km2 (DVCA1g circuit 9) in Fig. 1 is ftl[t
.

This second VCA
The output of the FM detection circuit 4 may be used directly without using the circuit 9. This is advantageous in terms of cost when it is difficult to distinguish the broadcast contents, such as i-information radio.

〔Effect of the invention〕

As described above, according to the present invention, high sensitivity can be achieved by using FM feedback, and high selectivity and high S/N can also be achieved at the same time.

4. Between the drawings, Figure 1 shows an example of heather/A Ming, and Figure 2 shows the detection characteristics of the level detection circuit in Figure 1.
Figure 1 shows the detection output characteristics at each point, Figure 4 shows the level detection characteristics when the level detection circuit in Figure 1 has a dead band and is set to f#4, and Figure 5 shows the conventional FM negative feedback circuit. FIG. :! 1 Bit...High frequency amplification circuit 2...Frequency change circuit 3...Filter 4...FM detection l! ! L path 5...Local oscillation circuit 6...I-th VCA circuit 7...-Level detection circuit 8...Level adjustment Lgl path 9...・Second VCAl road t# Sadato Pioneer Corporation FM building: ILshi Figure 3

Claims (2)

[Claims] (1) Negative feedback of the output of the FM detector to the local oscillator,
It is a so-called FM negative feedback receiver, and includes a level detector that detects the output level of the FM detector, and a voltage control amplifier whose level is controlled by the output of the level detector,
An FM receiving device characterized in that the output of the voltage control amplifier whose level is controlled according to the output level of the FM detector is applied to a local oscillator to control the amount of feedback to the local oscillator. (2) The FM receiving device according to claim 1, wherein the level detector has a dead zone.