JP3286518B2 - Electric field strength detection circuit of radio receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric field intensity detecting circuit of a radio receiver improved to obtain an electric field intensity detecting signal having good linearity.

[0002]

2. Description of the Related Art Conventionally, there has been known a circuit for detecting a received electric field intensity using an AGC signal as shown in FIG. FIG.
In the above, after the received RF signal is amplified by the RF amplifier circuit (1), the local oscillator circuit (3) in the mixing circuit (2)
And is converted to an IF signal. The IF signal is amplified by an IF amplifier circuit (4) and AM detected by an AM detection circuit (5). And A
An output signal of the M detection circuit (5) is amplified by a subsequent audio amplification circuit.

The output signal of the AM detection circuit (5) is I
Applied to the FAGC circuit (6) and the IFAGC circuit (6)
Amplifying circuit (4) by IFAGC signal generated from
Is controlled. When the level of the IF signal exceeds a predetermined level, the IF amplifier circuit (4) uses the IFAGC signal.
Is controlled so that the IF signal level becomes substantially constant. When the received electric field strength increases and the IF signal level further increases, the gain of the IF amplifier circuit (4) becomes minimum, the output signal level of the IF amplifier circuit (4) increases, and the IFAGC loop does not work. And IF
Immediately before the reception electric field strength at which the AGC loop becomes ineffective, an RFAGC signal corresponding to the output signal of the RF amplifier circuit (1) is generated from the RFAGC circuit (7). That is, when the received RF signal level exceeds a predetermined level, the RFAGC
A signal is generated. When the RF signal level increases, RFA
The GC signal increases, and the gain of the RF amplifier circuit (1) decreases. Therefore, the output signal level of the RF amplifier circuit (1) can be kept substantially constant. Therefore, the level of the IF signal applied to the AM detection circuit (5) is limited to a level not higher than the saturation level of the AM detection circuit (5) with respect to the received signal having a large input. it can.

The IFAGC signal and the RFAGC signal
The signals are added in an adding circuit (8). The output signal of the adding circuit (8) is generated as a signal indicating the electric field strength. RFAGC signal and IFAGC signal are RF
It is obtained by smoothing the output signals of the amplifier circuit (1) and the AM detection circuit (5), and the levels of the RF and IFAGC signals change as shown in FIG. Therefore, the output signal of the adder circuit (8) is as shown by the dotted line in FIG. 3A, and a signal indicating the electric field strength can be obtained.

[0005]

By the way, the radio receiver sweeps the reception frequency by changing the local oscillation signal, and stops the sweep when the broadcast station having the reception electric field strength equal to or higher than the detection level is received. And a search function for receiving the broadcast station. The determination as to whether or not the electric field strength of the broadcasting station is equal to or higher than the detection level is made based on whether or not the output signal level of the adding circuit (8) is equal to or higher than a predetermined level. However, there is a portion (a) in the output signal of the adder circuit (8) in FIG. 3A where the output signal level slightly increases with an increase in the electric field intensity. When the electric field strength detection level is provided in the portion (a), if the detection level changes due to a variation or the like, the electric field strength detection level of the broadcasting station greatly changes, and the broadcasting station cannot be detected with accurate electric field strength. There was a problem.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has an RF amplifier circuit for amplifying a received RF signal and a frequency converter for converting an output signal of the RF amplifier circuit into an IF signal. A circuit for detecting electric field strength of a radio receiver, comprising: a first circuit for detecting an output signal of the IF amplifier; and a first circuit for detecting an output signal of the first circuit. According to the output signal, the I
A first AGC signal generation circuit for generating a first AGC signal for controlling a gain of an F amplification circuit; an amplification circuit for amplifying an output signal of the frequency conversion circuit; and a second detection circuit for detecting an output signal of the amplification circuit A second AGC signal generation circuit for generating a second AGC signal for controlling a gain of the RF amplification circuit in accordance with an output signal of the second detection circuit; the first and second AGC signals; An adder circuit for adding an output signal to obtain an electric field intensity detection signal, wherein gains of the IF amplifier circuit and the amplifier circuit are controlled in opposite directions according to the first AGC signal.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an embodiment of the present invention. (9) and (10) show first and second IFs in which amplification factors change in opposite directions to amplify IF signals. An amplifier circuit, (11) a third IF amplifier circuit for amplifying an output signal of the first IF amplifier circuit (9), (12) a smoothing circuit (12a) for smoothing an output signal of the AM detector circuit (5), and a smoothing circuit A first AGC signal generation circuit including a comparison circuit (12b) for generating an IFAGC signal in accordance with the output signal of (12a); and (13) an AM detection circuit (13) for AM detection of an output signal of the second IF amplification circuit (10) 13a) and a smoothing circuit (13) for smoothing the output signal of the AM detection circuit (13a).
b) and RFA according to the output signal of the smoothing circuit (13b).
A comparison circuit (13c) for generating a GC signal;
The AGC signal generation circuit (14) is an addition circuit for adding the output signals of the first and second AGC signal generation circuits (12) and (13) and the output signal of the AM detection circuit (13a).

In FIG. 1, a received RF signal is amplified by an RF amplifier circuit (1), and then mixed with a local oscillation signal from a local oscillation circuit (3) in a mixing circuit (2).
A signal is generated from the mixing circuit (2). The IF signal is amplified by first and third IF amplifier circuits (9) and (11), and then AM detected by a detection circuit (5). The output signal of the detection circuit (5) is transmitted from an output terminal (16) to a subsequent circuit, and is also smoothed by a smoothing circuit (12a).
The electric field strength of the received signal is detected. Smoothing circuit (12a)
Is applied to the comparison circuit (12b), and when the level of the output signal is lower than the first reference level, the first AG
No IFAGC signal is generated from the C signal generation circuit (12). In this case, the gain of the first IF amplifier circuit (9) is the maximum gain, and the gain of the second IF amplifier circuit (10) is 0. No output signal is generated. Therefore, RF
-AGC operation is not performed at all.

Here, when the received electric field strength increases and the output signal level of the smoothing circuit (12a) exceeds the first reference level, the IFAGC signal is sent from the first AGC signal generation circuit (12) to the first and second IF amplification circuits. (9) and (1)
0). Then, in response to the IFAGC signal, the gain of the first IF amplifying circuit (9) decreases,
The gain of the F amplifier circuit (10) increases. Therefore, the first
The output level of the IF amplifier circuit (9) does not rise above a predetermined level. On the other hand, an output signal is generated from the second IF amplifying circuit (10) due to an increase in the gain of the second IF amplifying circuit (10), and the output signal of the second IF amplifying circuit (10) is output to the AM detection circuit (13a). It is detected. Then, the output signal of the AM detection circuit (13a) is smoothed by the smoothing circuit (13b). The output signal of the smoothing circuit (13b) is applied to the comparison circuit (13c), and the smoothing circuit (1
If the level of the output signal of 3b) is equal to or lower than the second reference level, the second AGC signal generation circuit (13) does not generate the RFAGC signal.

When a stronger input signal is applied, the IFAGC operation becomes ineffective and the output level of the AM detector (5) rises from a substantially constant level. At this time, the level of the output signal of the smoothing circuit (13b) is detected by the comparison circuit (13c) to be equal to or higher than the second reference level, and the second AGC signal generation circuit (13) outputs the RF signal.
Generate an AGC signal. The RFAGC signal is applied to the RF amplifier circuit (1), and the gain of the RF amplifier circuit (1) decreases according to the RF-AGC signal. Therefore, the output level of the RF amplifier circuit (1) is controlled so as not to become higher than a predetermined level.

Therefore, when the electric field strength of the received signal becomes higher than a predetermined level, the output level of the AM detection circuit (5) can be made substantially constant, and the AM detection circuit (5) can be prevented from being saturated. If the signal obtained by amplifying the output signal of the mixing circuit (2) by the second IF amplifying circuit (10) is used to operate the RF-AGC, the input signal of the comparing circuit (13c) is in proportion to the received electric field strength. Because it changes greatly, RFA
The operation start point of the GC can be set with high accuracy.

The output signals of the first and second AGC signal generation circuits (12) and (13) are applied to an addition circuit (14). Further, the output signal of the AM detection circuit (13a) is also applied to the addition circuit (14). By the way, IFA
The GC signal changes as shown in FIG. Since the output signal of the second IF amplifier circuit (10) is generated by the generation of the IFAGC signal, the output signal of the AM detection circuit (13a) is as shown in FIG. Further, since the RFAGC signal is generated at an electric field strength at which the IFAGC operation is no longer effective, FIG.
It occurs as shown in (b). Since the output signal of the adder circuit (14) adds the three output signals, it becomes a signal as indicated by a dotted line in FIG. As apparent from FIG. 3B, the output signal of the adder circuit (14) changes linearly with the received electric field strength.

[0013] Figure 4 is a diagram showing a specific circuit example of the first and second 2IF amplifier circuit of FIG. 1 (9) and (10), (1
6 ) and ( 17 ) are differentially connected transistors, ( 1)
8 ) and ( 19 ) are differentially connected, transistors having a common emitter connected to the collector of the transistor ( 16 ), ( 20 ) and ( 21 ) are differentially connected, and the common emitter is connected to the collector of the transistor ( 17 ). The connected transistors, ( 22 ) to ( 25 ), are transistors ( 1 )
8 ) to ( 19 ), current mirror circuits for inverting the collector currents, ( 26 ) and ( 27 ) are current mirror circuits for inverting the output currents of the current mirror circuits ( 24 ) and ( 25 ), and ( 28 ) is a reference. A reference voltage source for generating the voltage Vref, ( 30 ) is a diode to which the reference voltage Vref is applied to the cathode, and ( 31 ) and ( 32 ) are diodes (3)
0) is a resistor connected in series between the anode and the cathode.

In FIG. 4, when the output signal of the first AGC signal generation circuit (12) is not generated, the voltage obtained by dividing the anode-cathode voltage VD of the diode ( 30 ) is applied to the transistors ( 18 ) and ( 21 ). Is applied to
Since the terminal voltage VD of the diode ( 30 ) is about 0.7 V, if the voltage dividing ratio of the resistors ( 31 ) and ( 32 ) connected in series is set to 7: 1, the transistors ( 18 ) and ( 1 )
9 ) The difference voltage between the base voltages of the transistors ( 20 ) and ( 21 ) is 0.1 V
Thus, only the transistors ( 18 ) and ( 21 ) are turned on. The collector currents of the transistors ( 16 ) and ( 17 ) according to the RF signal applied to the base of the transistor ( 16 ) as an input signal are supplied to the current mirror circuit ( 22 ) and the transistors ( 18 ) and ( 21 ) via the transistors ( 18 ) and ( 21 ). ( 2
5) is applied and inverted. Further, the output current of the current mirror circuit ( 25 ) is applied to the current mirror circuit (28) and inverted. Then, the output currents of the current mirror circuits ( 22 ) and ( 27 ) are added, and the added output current is applied to the AM detection circuit (5) at the subsequent stage.

When an IFAGC signal is generated from the first AGC signal generation circuit (12), a collector current of the transistor ( 33 ) corresponding to the IFAGC signal is generated. The collector current ( 3
The connection midpoint voltages of 1 ) and ( 32 ) decrease, and the connection midpoints decrease, so that the transistors ( 18 ) and ( 19 ) and the transistors ( 20 ) and ( 21 ) have a linear pair of differential pairs. Work in the area. The collector current of the transistor ( 16 ) according to the input signal is the transistor ( 1)
8 ) and ( 19 ), the collector current of the transistor ( 17 ) is shunted to the transistors ( 20 ) and ( 21 ). The collector currents of the transistors ( 18 ) and ( 21 ) are supplied to subsequent circuits via current mirror circuits ( 22 ), ( 25 ) and ( 27 ). The collector currents of the transistors ( 19 ) and ( 20 ) are applied to the current mirror circuits ( 23 ) and ( 24 ) and are inverted. Furthermore, the output current of the current mirror circuit (24) is supplied to a current mirror circuit (26) is inverted. Then, the output currents of the current mirror circuits ( 23 ) and ( 26 ) are added,
The added output current is supplied to a second AGC signal generation circuit ( 12 ).
Supplied to By operating the differential pair in the linear region according to the IFAGC signal, the magnitudes of the output signals of the current mirror circuits (26) and (27) change in opposite directions.

[0016]

As described above, according to the present invention, the first
The gain of the second IF amplifying circuit increases according to the AGC signal of the AGC signal generating circuit, and the second AGC signal is amplified using the signal obtained by amplifying the output signal of the frequency conversion circuit by the amplifying circuit.
Since the signal generation circuit is operated and the output signal of the first and second AGC signal generation circuits and the output signal of the amplification circuit are added to generate a signal indicating the reception electric field intensity, the electric field intensity with good linearity is obtained. A detection signal can be obtained. Therefore,
At the time of the search operation, even if a variation occurs in the station detection level that determines the search stop, the intensity of the received electric field detected changes little, and the accurate search stop can be performed.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a characteristic diagram for explaining the present invention.

FIG. 4 is a circuit diagram showing a main part of FIG. 1;

[Explanation of symbols]

 Reference Signs List 9 first IF amplifier circuit 10 second IF amplifier circuit 11 third IF amplifier circuit 12 first AGC signal generation circuit 13 second AGC signal generation circuit 14 addition circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-62246 (JP, A) JP-A-4-223629 (JP, A) JP-A-1-208915 (JP, A) JP-A-1- 241932 (JP, A) JP-A-48-101549 (JP, U) Patent 3148540 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03G 3/30 H04B 1/16

Claims (1)

(57) [Claims] An RF amplifier circuit for amplifying a received RF signal;
A field strength detection circuit of a radio receiver comprising a frequency conversion circuit for converting the output signal into an IF signal, and the 1 IF amplifying circuit for amplifying the IF signal, of the RF amplifier circuit, the first 1I F amplifier A first detection circuit for detecting an output signal of the circuit; a first AGC signal generation circuit for generating a first AGC signal for controlling a gain of the first IF amplification circuit in accordance with the output signal of the first detection circuit; A second IF for amplifying the IF signal from the frequency conversion circuit
An amplification circuit; a second detection circuit for detecting an output signal of the second IF amplification circuit; and a second generation circuit for generating a second AGC signal for controlling a gain of the RF amplification circuit in accordance with the output signal of the second detection circuit. 2
An AGC signal generation circuit; and an addition circuit for adding the first and second AGC signals and the output signal of the second detection circuit to obtain an electric field strength detection signal . 1 IF
An electric field strength detection circuit for a radio receiver , wherein gains of an amplifier circuit and the second IF amplifier circuit are controlled in opposite directions.