JPS6238356Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an input level detection circuit for an FM receiver whose input level fluctuates significantly, such as an FPU/STL/TSL receiver.

Conventionally, in order to calibrate the input level in this type of receiving device, the gain of the receiving device is set to a certain value using MGC (manual gain control), the RF output level is detected, and the input level is calibrated using the output current or voltage. I was gone. Therefore, there was a drawback that input level calibration could not be performed under standard usage conditions in AGC. Also, if the input level of the receiver is abnormally low for a certain value of MGC, it cannot be detected, and if the input level is too high, the amplifier before the detector becomes saturated, making it impossible to detect the input level. That is, the conventional technical method has the disadvantage that the input level calibration range is very narrow.

The purpose of the present invention is to calibrate the input level of the receiver while it is in AGC operation, that is, to calibrate the input level under standard operating conditions, and to extend the range of calibration to the usable range of the receiver.

In a receiver equipped with AGC, each part of the amplifier operates without saturation. Furthermore, the RF output to which AGC is applied changes slightly with respect to the set value level of AGC. This change causes input level fluctuations.
This is a minute change suppressed by the AGC lube gain, and corresponds to input level fluctuations. The present invention attempts to detect the input level by detecting and amplifying only this minute change. That is, the RF output multiplied by the AGC is detected and applied to one input of the differential DC amplifier, and a voltage corresponding to the DC component of the set value of the AGC is applied to the other input. By reading the differential DC amplifier output at this time, the input level can be calibrated and detected.

Referring to FIG. 1, one embodiment of the present invention is as follows:
An RF signal input terminal 10, a variable gain element 11 connected to this input terminal 10, an RF signal amplifier 12, an RF signal output terminal 13, a detector 14 for detecting the output, and a detector 14 for detecting the output. A DC amplifier 15 for amplification and a detector 1 for detecting the output 13
4, an AGC DC amplifier 15, a detector 16 that detects the AGC output 13, a reference voltage (Er) source 17, and the output of the detector 16 and the reference voltage Er.
and a direct current output terminal 19 for input level calibration.

Next, as shown in FIG. 2, in the AGC range (receivable range) D, the AGC multiplied output 13 increases slightly as the input level increases to 10. When this output is detected by the detector 16 and the DC output is applied to one side of the amplifier 18, and a certain reference voltage Er is applied to the other side, a DC output linearly proportional to the input level is obtained as shown in Figure 3. It will be done.

As explained above, in the present invention, by detecting and amplifying the RF output multiplied by AGC, the input level can be linearly displayed as a display output over a wide range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention. FIGS. 2 and 3 are diagrams explaining the operation of an embodiment of the present invention.

Claims (1)

[Scope of utility model registration request] In an FM receiving device having an AGC circuit, there is provided a detector that detects the output of the AGC circuit with input level fluctuations compressed to detect a signal level, and the output level of the detector corresponds to the level setting value in the AGC circuit. An input level detection circuit comprising: a differential DC amplifier that receives a voltage, and detects an input level to the FM receiving device based on an output of the differential DC amplifier.