JPH0161245B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a high-performance radio receiving circuit that reduces signal distortion even when receiving a large input signal, and an object of the present invention is to provide an excellent automatic gain control (AGC) circuit with a particularly simple configuration. That is. Another purpose is to use an intermediate frequency amplification circuit that can be used commonly for AM/FM signals, making it easy to switch between AM and FM reception, and to extract the signal level detection signal also when receiving AM/FM. It is to do so.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A radio receiving circuit according to the present invention will be described below with reference to drawings of an embodiment. FIG. 1 is an electrical connection diagram of one embodiment of the radio receiving circuit of the present invention, in which 1 is a frequency conversion circuit for AM signals, 2 is a frequency conversion circuit for AM signals;
is a local oscillation circuit used for frequency conversion circuit 1, and 3 is a local oscillation circuit used for frequency conversion circuit 1.
4 is an AM detection circuit, 5 is an FM intermediate frequency amplification circuit, and 6 is an FM detection circuit.

In FIG. 1, first, the operation during AM reception will be explained. When the switch 24 is turned on to the AM side terminal a, AM operation will be performed. That is,
The signal tuned by the antenna coil 13, variable capacitor 11, and capacitor 12 is applied to the AM frequency conversion circuit 1. On the other hand, the local oscillation circuit is coil 1
9, a tuning circuit consisting of a variable capacitor 17 and a capacitor 18, and transistors 205 and 202 for local oscillation connected to the secondary winding of the coil 19, a resistor 214, the base and emitter of the transistor 202, and a resistor 203. , 204, and the emitter and collector of the transistor 205 are amplified in the same phase to create a positive feedback loop and oscillate. The local oscillation signal obtained here is transmitted to the transistor 103 of the frequency conversion circuit 1 via the emitter follower composed of the transistor 201.
, then transistors 102 and 10
3 operates as an emitter-coupled differential amplifier, and oscillation outputs with opposite phases are output to the collectors of transistors 102 and 103, and this signal is sent to the emitters of frequency conversion transistors 104 and 105 and the emitters of transistors 106 and 107. Added. On the other hand, the signal received by antenna coil 13 is applied to the bases of transistors 104 and 107. Since the transistors 104 and 105 and the transistors 106 and 107 are emitter-coupled, the oscillation signal from the emitter and the received signal from the antenna coil 13 are mixed with each other, and the output thereof is connected to the collectors of the transistors 105 and 107. The output signal is output as an intermediate frequency signal to the secondary side of the intermediate frequency coil 15. This intermediate frequency signal is then applied to the base of the transistor 301 of the intermediate frequency amplification circuit 3 via the capacitor 16 and the resistor 20. The intermediate frequency amplification circuit 3 includes transistors 301, 302, 312, 313, 321,
322, and the signals amplified by these differential amplifiers are applied from the collectors of transistors 321 and 322 to the bases of AM detection transistors 401 and 402. .

A capacitor 29 is connected to the emitters of the AM detection transistors 401 and 402, and the transistors 401 and 4 are connected to both ends of the capacitor 29.
A signal detected by AM by 02 appears. The signal is then guided to the AM detection output terminal through a low-pass filter constituted by a resistor 30 and a capacitor 31. In addition, resistors 316, 317,
318 is a DC bias negative feedback resistor, and capacitors 22 and 23 are bypass capacitors.

The above operation is the operation when the input signal is small, and next, the operation when the input signal is large will be explained.

Current is supplied by a transistor 306 to differential amplification transistors 301 and 302 constituting the intermediate frequency amplifier, and frequency conversion transistors 104, 105, 106, 107, 102, 1
03 is supplied with current by a transistor 109. When the input signal is small, the DC voltage appearing on the output side of the AM detection transistors 401, 402 is relatively small, but when the input signal is large, the DC voltage appearing on the output side of the AM detection transistors 401, 402 becomes large. +B power supply voltage is 10V
If so, the transistor 40 for AM detection
The base voltage of transistor 1,402 is 9.5V, and the emitter of transistor 401,402 when there is no signal is 8.8V. (The contact potential between the base and emitter is 0.7V.) On the other hand, if the value of the resistor 418 is set so that the voltage drop across the resistor 415 is 0.3V, and the current of the transistor 417 is set,
Since the contact potential of diode 416 is approximately 0.7V, the base of transistor 412 will be approximately 9.0V. On the other hand, the base of the transistor 411 is about 8.
Since the voltage is 8V, the base of the transistor 411 is 0.2V lower than the base of the transistor 412, so the transistor 411 becomes conductive and the transistor 412 is turned off. Therefore,
The voltage drop across resistor 413 becomes zero, transistors 305 and 123 are both cut off, and transistor 3
06 and 109 both become conductive. However, when receiving a small input signal to receiving a large input signal,
The DC voltage between the emitters of the AM detection transistors 401 and 402 and the base of the transistor 411 becomes higher than the current 8.8V to 9.0V.
When this happens, the transistor 411 gradually changes from a conductive state to a cut-off state, and the transistor 412
changes from a cut-off state to a conduction state. Then resistance 41
As the value of the voltage drop of 3 increases, the transistor 305 changes from a cut-off state to a conduction state. The base of transistor 306 is biased to approximately 1.1V. This is 2 of diodes 419 and 420.
The voltage of 1.4V of each diode is divided by a resistor 308, a diode 332, and a resistor 309, and the base of the transistor 306 is set to about 1.1V. This diode 332 is provided to ensure temperature by making the contact potential which changes with temperature almost the same as the contact potential between the base and emitter of the transistor 306 which changes with temperature. Therefore, when the voltage of the resistor 413 becomes higher than 1.1V, the transistor 305 becomes conductive and the transistor 306 becomes cut off. Then, since the currents in the transistors 301 and 302 of the intermediate frequency amplifier are reduced, the gain of the intermediate frequency signal is reduced, and the amplitude of the signals at the collectors of the transistors 321 and 322 can be kept to a not very large amplitude. If the emitter of the transistor 305 and the emitter of the transistor 306 are connected directly without using the resistor 331, current will flow rapidly when the transistor 305 becomes conductive, making it impossible to obtain a linear AGC effect according to the input signal level. 305
The base potential (voltage of resistor 413) of resistor 307
The voltage does not rise above the sum of the voltage drop and the voltage between the base and emitter of the transistor 305.

Therefore, as in the above embodiment, the transistor 305
When a resistor 331 is connected between the emitter of the transistor 306 and the emitter of the transistor 306, an AGC effect corresponding to the DC voltage of the detection output can be obtained due to the voltage drop of the resistor 331, and the voltage of the resistor 413 is also
It is possible to take out the voltage higher by the voltage drop of 1.

Also, the base potential of the transistor 109 is the voltage of the two diodes 211 and 212.
1.4V with resistor 111, diode 112, resistor 1
It is divided and set by 13.

Here, the diode 112 is for temperature guarantee as described above.

The set value of the base potential of the transistor 109 is set at a point where the input signal level increases, the current of the transistor 306 gradually increases, and the gain of the intermediate frequency amplifier becomes uncontrollable, and the voltage of the resistor 413 is set to approximately
If it is a point of 1.6V, the transistor 123,
The base potential of the transistor 109 is set to be approximately 1V, assuming that the sum of the voltages between the base and emitter of the two transistors 124 is 1.3V, and the voltage of the resistor 110 is 0.3V. Due to the increase in the input signal, the gain control of the intermediate frequency amplifier becomes impossible, and the intermediate frequency signal applied to the detection circuit becomes even larger, and the DC voltage of the detection output also becomes higher.The voltage of the resistor 413 also increases, and when it becomes 1.6V or more, the transistor 12
The base potential of transistor 4 becomes higher than the base potential of transistor 109, and transistors 123 and 124
becomes conductive, the current in the transistor 109 decreases, and the transistors 102 and 102 of the frequency conversion circuit 1 become conductive.
The currents of 103, 104, 105, 106, and 107 are reduced, operating to reduce the gain of the frequency conversion circuit. Further, a current mirror circuit is provided at the collector of the transistor 124, and this current mirror circuit is composed of a diode 125 and PNP transistors 126 and 127.
4,105 emitter and transistor 106,1
When connected to the emitters of transistors 07 and 1, transistors 126 and 127 become conductive when the input signal becomes large, making the emitter potential of transistors 104 to 107 positive and reducing the current of transistors 104 to 107.
Due to the decrease in the current of 09, transistor 104~
Since it is possible to reduce the current to a greater extent than by reducing the current of 107, even a large input signal can be made into a reduced signal and a signal without distortion can be extracted.

The characteristics at this time are shown in FIG. The output level is from point A to transistor 30 of the intermediate frequency amplification circuit.
Starting with the AGC operation of 5,306, the current of the transistor 306 is gradually reduced due to the voltage drop across the resistor 331. Therefore, AGC operation starts from the base of transistor 305 at 1.1V,
The voltage drop of the resistor 331 is used until the base potential reaches 1.6V at the input level point B, and the AGC operation of the frequency conversion circuit is performed by the transistors 123 and 124 at 1.6V or higher.

The reason why the base voltage of the transistor 306 is set to a voltage lower than the operating level of the transistor 123 is to speed up the AGC operation of the intermediate frequency circuit.
This is to slow down the AGC operation of the frequency conversion circuit.

If the AGC operation of the frequency conversion circuit is made faster,
If the AGC operation of the intermediate frequency amplifier is slowed down, the S/N will be poor as shown in FIG. 3B. This is because the gain of the frequency conversion circuit is lowered while the S/N is poor, so the S/N cannot be improved. This allows the intermediate frequency amplification circuit to
The AGC operation of the frequency conversion circuit is performed after the S/N becomes good after performing the AGC operation. Therefore, in the above embodiment, FIG.
As shown in the figure, a signal with good S/N ratio can be obtained.

Next, FM operation will be explained. During FM operation, switch 24 is turned to side b. switch 24
By supplying power from the b-side terminal of the FM tuner section (not shown), the signal received by the tuner is converted to an intermediate frequency signal, and the intermediate frequency signal (10.7 MHz in this case) is added to point A. The signal at point A is applied to intermediate frequency amplifier 3 via resistor 21. The signal applied to the intermediate frequency amplifier 3 is transmitted through transistors 301, 302, which constitute a differential amplifier.
312, 313, 321, 322, and further from the collectors of transistors 321, 322.
Transistor 505, 5 of FM intermediate frequency amplifier 5
06 and amplified here.

And its output is the transistor 505,5
Transistors 509, 510 from the collector of 06
The signal is applied by transistors 522 and 523 forming the FM detection circuit 6 via the FM detection circuit 6.

On the other hand, the phase is changed from the emitter of the transistor 510 by a phase changing capacitor 511 and applied to the base of a transistor 524. A tuning circuit 25 is provided between this base and +B, and it is tuned to the intermediate frequency (10.7 MHz) and changes the phase to positive or negative by the frequency change by FM modulation from the intermediate frequency. This phase change capacitor advances the phase of the signal at the emitter of the transistor 510, and the tuning circuit 25 turns the frequency change into a positive and negative phase change around this. This signal is transmitted from the emitter of transistor 524 to transistor 525,
In addition to 528, one transistor 510, 509
The signal at the emitter of transistor 52 is in opposite phase.
The transistors 522, 523 are turned on and off with opposite polarity, and the collectors of the transistors 522, 523 are connected to the emitters of the transistors 525, 526 and 527, 528. 527,
528 turns on and off, transistors 525,5
By multiplicative switching with 26 ON-OFF
The FM signal is detected and taken out to the resistor 529 at the collector of the transistors 526 and 528, and the detected output signal can be taken out from the capacitor 27 as a bypass.

At this time, since the switch 24 is set to the b side,
Since no voltage is applied to AM frequency conversion circuit 1 and local oscillation circuit 2, AM operation of 1 and 2 is not performed.
Only FM works. On the other hand, during AM operation, voltage is applied to the base of the transistor 542 via the resistor 543, so the transistor 542 is turned on, and the transistors 507, 512, 513, 516, 51
8,520 is turned off, and the FM intermediate frequency amplification circuit 5 and the FM detection circuit 6 do not operate. Transistors 507 and 51 during FM operation
2,513, 516, 518, and 520 are turned on, and the FM intermediate frequency amplification circuit 5 and the FM detection circuit 6 come into operation. Therefore, it has the advantage of requiring fewer FM and AM switching circuits.

Also, at this time, since the collector of the transistor 305 is connected to the AM power supply via the resistor 210, the transistor 305 does not operate during the FM operation, so a constant current flows through the transistor 306, and the AGC operation does not occur. When receiving FM, the AM detection transistors 401, 402, 411, and 412 operate, and when the input signal becomes large, a large DC voltage signal can be extracted from both ends of the capacitor 28, which can also be used as a signal for a tuning indicator.

At this time, the collector of transistor 123 is
Since the voltage is supplied both during the FM mode and the FM mode, the base voltage of the transistor 123 can extract a high DC voltage.

If the voltage of the frequency conversion circuit is shared so that no voltage is applied to the collector of the transistor 123 during FM, even if a large voltage is to be output across the capacitor 28, the forward characteristic of a diode will flow from the base of the transistor 123 to the collector. The disadvantage is that the current flows and the voltage does not rise above 0.7V. Therefore, the collector of the transistor 123 is connected to +B of the intermediate frequency amplification circuit via a resistor 130 so as to supply voltages in both FM and AM. As a result, the transistor 123 operates with a small base current, so a voltage greater than 0.7V can be taken out across the capacitor 28 even during FM. and inside the dashed line
It has the feature that it can be easily configured by converting it into an IC.

As explained above, the present invention can configure a receiving circuit with low distortion even with large input signals, and furthermore,
It has many advantages, such as being able to easily switch signals and extracting a signal level detection signal at a high level even when receiving FM.

[Brief explanation of drawings]

FIG. 1 is an electrical connection diagram of an embodiment of the radio receiving circuit of the present invention, and FIGS. 2 and 3 are explanatory diagrams for explaining the characteristics of the embodiment. 1...Frequency conversion circuit for AM signal, 2...Local oscillation circuit, 3...Intermediate frequency amplification circuit for both AM and FM, 4...AM detection circuit, 5...FM intermediate frequency amplification circuit, 6... FM detection circuit.

Claims (1)

[Claims] 1 FM tuner, AM tuner consisting of frequency conversion circuit and local oscillation circuit, and AM/FM tuner
An intermediate frequency amplification circuit for both AM and FM, which is composed of multiple stages of differential amplifiers that amplify the output signals from the FM tuner and AM tuner selected by the changeover switch, and this intermediate frequency amplification circuit for both AM and FM. AM detect the output signal from
It is equipped with an AM detection circuit and a parallel circuit consisting of a capacitor and a resistor for detecting the level of the detection output signal from this AM detection circuit, and the intermediate frequency amplifier circuit for both AM and FM is connected to the power source of the differential amplifier. A second transistor is provided, the emitter of which is connected to the emitter of a certain first transistor via a resistor, the level signal from the parallel circuit is applied to the base, and which is activated only when receiving AM;
The frequency conversion circuit of the AM tuner is emitter-coupled to the emitter of the third transistor that is its power source, and the level signal from the parallel circuit is applied to the base, and the operating voltage is higher than the operating voltage level of the second transistor. is set to the level,
And regardless of the above AM/FM switch
A radio receiving circuit equipped with a fourth transistor that is activated when receiving both AM and FM.