JPS6355817B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to radio receivers and other receiving circuits, and has a simple structure to reduce signal distortion when receiving a large input signal, significantly improve S/N, and quickly operate AGC. The purpose of this is to provide an excellent receiving circuit that can perform the following functions.

Another purpose is to make AM/FM switching extremely easy by using an intermediate frequency amplification circuit that shares AM and FM signals.

An embodiment of the receiving circuit of the present invention will be described below with reference to the drawings. In the figure, 1 is
AM signal frequency conversion circuit, 2 is a local oscillation circuit that outputs a local oscillation output to be added to this frequency conversion circuit 1, 3 is an intermediate frequency amplification circuit for AM and FM, 4
is AM detection circuit, 5 is FM intermediate frequency amplification circuit, 6 is
is an FM detection circuit.

First, we will explain the operation during AM reception. When switch 24 is turned to side a and turned on,
AM mode is activated. The received signal tuned by the antenna coil 13, variable capacitor 11, and capacitor 12 is applied to the frequency conversion circuit 1 for both AM and FM. On the other hand, the local oscillation circuit 2 has a tuning coil 19
The secondary winding of transistor 2 in local oscillation circuit 2
02 and the base of the transistor 205 via a resistor 214, so that the output appearing at the secondary winding of the coil 19 is connected to the resistor 21.
4. Base of transistor 205. The emitter resistors 204 and 203, the emitter resistor of the transistor 202. It is amplified in the same phase as the collector, creating a positive feedback loop and oscillating. This transmission signal is applied to the transistor 103 of the frequency conversion circuit 1 via the emitter follower of the transistor 201. Then, transistors 103 and 102 operate as an emitter-coupled differential amplifier, and transistors 103 and 1
The oscillation outputs with mutually opposite phases are taken out to the collectors of 02 and frequency conversion transistors 104 and 10
An oscillation signal is applied to the emitters of transistors 106 and 107. On the other hand, the signal received by the antenna coil 13 is transmitted to the transistors 104 and 10.
7 and the transistor 104,1
05, 106, 107 are mixed with the oscillation signal from the emitters coupled to each other, and the transistor 1
An intermediate frequency signal is taken out to an intermediate frequency coil 15 connected to the collector of 05, 107, and applied to the base of a transistor 301 of an intermediate frequency amplifier circuit 3 via a capacitor 16 and a resistor 20. The intermediate frequency signal to this intermediate frequency amplification circuit 3 is transmitted to transistors 301, 302, 312, 313 and 321, 3.
22, and from the collectors of transistors 321 and 322 to the bases of AM detection transistors 401 and 402,
AM detection is performed by transistors 401 and 402 whose emitters are connected to each other and a capacitor 29, and an AM detection output is taken out through a low-pass filter made up of a resistor 30 and a capacitor 31. At this time, resistors 317, 318, and 316 are DC bias negative feedback resistors, and capacitors 22 and 23 are bypass capacitors.

The above is an operation for a small signal, and the case of a next-largest input signal will be explained. When receiving a small signal, the differential amplification transistor 30 of the intermediate frequency amplification circuit 3
1,302 is supplied with current by a transistor 306, and the transistor 10 for frequency conversion
Current is supplied to transistors 4, 105, 106, 107, 102, and 103 by a transistor 110. When a small signal is received, the detected DC voltage obtained by the AM detection transistors 401 and 402 is small, but when a large input signal is received, the detected DC voltage value increases and becomes a higher voltage than when a small signal is received. Assume that the voltage of +Vcc is 10V, resistor 319,
Assuming that the voltage drop across 320 is 0.5V, the base voltage of AM detection transistors 401 and 402 is 9.5V. When there is no signal, the bases of transistors 401 and 402. If the contact potential between the emitters is approximately 0.7V, this emitter will be 8.8V.
becomes. On the other hand, 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.
The contact potential of transistor 412 is about 0.7V.
The base of is approximately 9.0V. transistor 411
Since the base of transistor 411 is about 8.8V, the base of transistor 411 is higher than the base of transistor 412.
0.2V low, so transistor 411 is on and transistor 412 is off.

Therefore, no current flows through the transistor 413. However, the collector point of transistor 412
423 applies a voltage (approximately 1.4V) stabilized by diodes 419 and 420 via resistor 422 and divides it by resistor 413, and
123 is set to a voltage (0.7V in this case) that does not conduct. The base of transistor 306 is approximately
Biased at 1.2V, the base of transistor 110 is applying a voltage of approximately 1.4V. Therefore, the transistor 305 becomes conductive from about 1.2V, and the transistor 123 starts conducting from about 1.4V. Therefore, when the input signal is small, transistors 305 and 123 are cut off and transistors 306 and 110 are turned on. However, when receiving a large input signal from receiving a small input signal, the emitters of the AM detection transistors 401 and 402 change. transistor 4
The DC voltage of the base of 11 has become higher, and the
As the voltage increases from 8.8V to higher than 9.0V, the transistor 411 gradually changes from the conductive state to the cutoff state, and the transistor 412 gradually changes from the cutoff state to the conductive state. Then, the value of the voltage drop across the resistor 413 increases, and the transistor 305 changes from a cut-off state to a conduction state. The base of transistor 306 is biased to approximately 1.2V. This is the voltage of about 1.4V across the two diodes 419 and 420, divided by the resistors 308 and 309, and then connected to the transistor 30.
The base of 6 is set to about 1.2V. Furthermore, the base of the transistor 110 is connected to two diodes 21.
2,213 voltage of 1.4V is applied. Therefore, when the voltage drop across resistor 413 becomes higher than 1.2V, transistor 305 becomes conductive and transistor 306 becomes conductive.
becomes in a state of interruption. Then, since the currents in the transistors 301 and 302 of the intermediate frequency amplifier circuit 3 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 suppressed to a not very large amplitude. When an input signal is further input, the transistor 306 is completely cut off, making it impossible to control the gain of the intermediate frequency amplifier circuit 3, and the intermediate frequency signal applied to the detection becomes even larger, the detected DC voltage also becomes higher, and the voltage across the resistor 413 increases. will also be higher. and resistance 4
When the voltage drop across transistor 13 becomes 1.4V or more, transistor 123 becomes conductive, and transistor 110 becomes conductive.
The current of transistors 102, 103, 104, 105, 106, 1 of frequency conversion circuit 1 decreases.
07 is reduced, the gain of the frequency conversion circuit 1 is reduced, and the intermediate frequency signal applied to the detection circuit 4 is controlled to a certain value, thereby making it possible to extract a distortion-free detection output even when a large input signal is present. The characteristics at this time are shown in FIG. At the output level, the transistors 305 and 306 of the intermediate frequency amplification circuit 3 are
AGC starts operating and frequency conversion circuit 1 starts from point B.
The AGC operation of the transistors 110 and 123 starts. Therefore, the distortion can be detected with a small value. At this time, the resistor 12 in the frequency conversion circuit 1
Reference numerals 1 and 122 act to make the emitters of transistors 104 to 107 a positive current when the current of transistor 110 decreases, making it easier to completely shut off transistors 104 to 103 and increasing the gain reduction effect. . The reason why the base voltage of the transistor 306 is made lower than that of the transistor 10 is also to speed up the AGC operation of the intermediate frequency amplifier circuit 3 and slow down the AGC operation of the frequency conversion circuit 1. If AGC of frequency conversion circuit 1
If the operation is made faster and the AGC of the intermediate frequency amplification circuit is made to operate later, the S/N becomes poor as shown by curve B in FIG. This is S/
If the gain of the frequency conversion circuit 1 is lowered while N is poor, the S/N will not improve. From this, the gain control (AGC) of the intermediate frequency amplification circuit 3 is performed early to improve the S/N, and then the frequency conversion circuit 1 is
This allows AGC to operate. Therefore, in this circuit, S/
N good signals can be obtained. Also, resistor 21
1,124 is a current limiting resistor.

Further, a voltage is applied to the collector 423 of the transistor 412 to the extent that the transistors 305 and 123 do not become conductive even when a small power signal is generated. This is because when the input signal suddenly changes from a small input signal to a large input signal, transistors 305 and 123 become conductive and the AGC
The disadvantage is that it takes a long time to start operating. This is because the transistor 305 does not become conductive unless the transistor 412 becomes conductive and the capacitor 28 is charged from 0 voltage to 1.2V. But 423
For example, if a voltage of 0.7V is applied to the point, 0.7V is applied to the capacitor 28 by the transistor 412.
Transistor 30 by simply charging from to 1.2V
5 conducts and performs AGC operation, so it has the characteristic of being able to perform fast operations. Even if the capacitance value of the capacitor 28 is made small, the AGC operation can be performed quickly, but the effect of removing the signal component passed through the transistor 412 becomes less and the distortion increases. Therefore, the capacitor 28 cannot be made smaller. In this example, the value is the same as that of the capacitor 28, and a faster AGC operation can be performed. Next, FM operation will be explained. By turning on the switch 24 to the b side, power is supplied from the b side to the FM tuner section. This switching converts the signal received by the tuner section into an intermediate frequency signal (here,
10.7MHz) is added to point A. The signal at point A is resistor 2
1 to the intermediate frequency amplification circuit 3, as well as three differential amplifier transistors 301, 302, 31.
2, 313, 321, and 322, and from the collectors of transistors 321, 322 to the collectors of transistors 505, 506 of the FM intermediate frequency amplification circuit 5, the transistor 509 of the FM detection circuit 6,
It is added to the base of 510. It is applied to transistors 522 and 523 constituting the FM detection circuit 6 from the emitters of transistors 509 and 510, and the phase is changed from the emitter of transistor 510 by a phase changing capacitor 511 and applied to the base of transistor 524. This transistor 52
A tuning circuit 25 is provided between the 4 base and +Vcc, and is tuned to an intermediate frequency signal of 10.7 MHz, and changes the phase to positive or negative by frequency change due to FM demodulation from the intermediate frequency. The phase change capacitor 511 advances the phase of the signal at the emitter of the transistor 510, and the tuning circuit 25 changes the phase around this at a frequency that changes from positive to negative. This signal is applied to transistors 525 and 528 from the emitter of transistor 524, while the signals at the emitters of transistors 510 and 509 are in opposite phase and transistors 522 and 523 are of opposite polarity.
ON-OFF, this transistor 322, 523
The collector of transistors 525, 526 and 52
In addition to 7,528 emitters, 52 transistors
transistor 52 differentially by a signal from 4
5,526 and 527,528 are turned ON and OFF, FM detection is performed by multiplicative switching of ON and OFF of transistors 525 and 526, and the signal is taken out to the resistor 529 of the collector of transistors 526 and 528, bypassed with capacitor 26, and detected. The output signal can be taken out from the output end 27. At this time, the base of the transistor 524 is +
Tuning circuit 2 from +Vcc so that it has the same potential as Vcc.
It is connected by the coil inside 5. Therefore, the bases of transistors 525 and 522 connected to the emitter of transistor 524 are 0.7V higher than +Vcc.
Low voltage. A diode 530 is provided to apply approximately the same voltage to transistors 526 and 527, and current flows through transistor 520. This diode 530 operates in the same way even if the base and collector of the transistor are set to +Vcc and the emitter is connected to the transistors 526 and 527. At this time, since the switch 24 is turned to the b side, no voltage is applied to the AM frequency conversion circuit 1 and the local oscillation circuit 2, so no AM operation is performed.
Only FM can be operated. Also, at this time, the collector of the transistor 305 is connected to the power supply of the AM frequency conversion circuit 1 and the local oscillation circuit 2 via the resistor 211, so the current of the transistor 306 is constant during FM operation, and the AGC operation is prevented. There is. Even when receiving FM, the AM detection transistors 401 and 402 operate, and the transistors 411 and 412 also operate, and when the input signal becomes large, a DC voltage signal can be extracted from both ends of the capacitor 28, so it is used as the instruction number of the tuning indicator. It can also be used. On the other hand, during AM operation, voltage is applied to the base of transistor 543 via resistor 542, so transistor 543
Turn on transistors 507, 512, 513,
516, 518, and 520 are turned off, and the FM intermediate frequency amplification circuit 5 and the FM detection circuit 6 do not operate.
During FM, no voltage is applied to the base of the transistor 543, so the transistor 507,
512, 513, 516, 518, 520 are ON
Thus, current flows so that the FM intermediate frequency amplification circuit 5 and the FM detection circuit 6 operate. Therefore, it has the advantage of requiring fewer switch circuits for switching between FM and AM. There is an advantage that it is easy to convert the area within this dashed line into an IC.

As described above, the present invention has the advantage of reducing the distortion signal when receiving a large input signal, significantly improving the S/N ratio, and enabling fast AGC operation.

[Brief explanation of drawings]

FIG. 1 is an electrical connection diagram showing one embodiment of the receiving circuit of the present invention, and FIGS. 2 and 3 are diagrams explaining its operation. 1 is an AM frequency conversion circuit, 2 is a local oscillation circuit, 3 is an AM/FM intermediate frequency amplifier, 4 is an AM detection circuit, 5 is an FM intermediate frequency amplifier, and 6 is an FM detection circuit.

Claims (1)

[Claims] 1. An intermediate frequency amplification circuit having at least two or more differential amplification circuits, and an emitter of a first transistor that supplies current to the differential amplifier constituting this intermediate frequency amplification circuit. the second connected to each other
and a fourth transistor whose emitters are mutually coupled to the emitters of a third transistor that supplies current to the AM frequency conversion circuit, and the bases of the second transistor and the fourth transistor are connected to the second and fourth transistors. The fourth transistor is configured to apply a DC voltage to such an extent that it does not conduct, and to apply a DC signal that changes depending on the output of the AM detection circuit to control the gains of the intermediate frequency amplification circuit and the AM frequency conversion circuit. The base bias of the first transistor is set to a lower voltage than the base bias of the third transistor, so that the gain control of the intermediate frequency amplifier circuit is performed prior to the gain control of the AM frequency conversion circuit. receiving circuit. 2. The receiving circuit according to claim 1, wherein the intermediate frequency amplification circuit is also used for FM, and the second transistor is configured to be inactive during FM operation.