JPS61264904A - Frequency conversion circuit - Google Patents

Abstract

PURPOSE:To improve the performance by applying a signal to a base of a transistor (TR) for a differential amplifier for amplification and extracting the amplified signal to an intermediate frequency filter with no adjustment from one of TRs via an output circuit having a low impedance. CONSTITUTION:A local oscillation signal of a local oscillation circuit is fed to a base of TRs 11, 14 via a resistor 20, a signal fed to emitters of TRs 11, 12 and 13, 14 is switched to extract two signals with opposite polarity to each other subjected to frequency conversion at a connecting point 85 of collectors of the TRs 11, 13 and at a connecting point 86 between collectors of the TRs 12, 14 and they are fed to bases of TRs 31, 32 for differential amplifier via capacitors 17, 18 and amplified. A signal amplified by the collector of TRs 32, 34 is fed to a base of an emitter follower TR 38 and an intermediate frequency signal is extracted at the intermediate frequency filter via a resistor 40 from the emitter of the TR 38. Thus, the intermediate frequency is adjusted with the good S/N and sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a frequency conversion circuit used in radio receivers and the like.

2. Description of the Related Art In recent years, radio reception circuits including frequency conversion circuits have been integrated into ICs. An example of a conventional frequency conversion circuit will be described with reference to the drawings.

FIG. 5 shows an electrical connection diagram of a frequency conversion circuit of a conventional receiving circuit. In FIG. 5, 1 is an IC frequency conversion circuit, 2 is an intermediate frequency signal amplifier, 3 is a detection circuit, 6 is an antenna coil, 5.62 is a variable capacitor, 56 is an intermediate frequency transformer, 65 is an intermediate frequency filter, 63 are local oscillation coils/7, 9, 10, 11.12, 13.14
, 24° 26 are transistors, 4, 7, 64.51 are capacitors, 8, 19, 20.90 are resistors, and 21, 22° 23 are current sources.

The operation of the frequency conversion circuit configured as described above will be explained below.

Antenna e, capacitor 4. The input signal tuned by the variable capacitor 6 is applied to the base of one of the transistors 9 and 1o whose emitters are connected to each other, and also to the base of the transistor 9.
, 1o to the emitters of transistors 11.12 and 13.14, as well as transistors 24.25 and A153. A local oscillation signal of a local oscillation circuit composed of a capacitor 51 and a tuning circuit of a variable capacitor 52 is transmitted to a transistor 1 via a resistor 20.
In addition to the base of 1.14, transistors 11.12 and 1
The signal applied to the emitter of 3.14 is switched, the intermediate frequency signal is taken out to the intermediate frequency transformer 56 connected to the collector of the transistor 11.13, and the intermediate frequency signal is added to the intermediate frequency amplifier 2 via the ceramic filter 55 for amplification. The detection circuit 3 detects the signal, and the detected signal is taken out to the terminal 71.

Problems to be Solved by the Invention However, in the above configuration, the primary impedance of the intermediate frequency transformer 66 is as high as 20 to 3 KΩ, and the impedance of the filter 55, such as a ceramic filter, is low and is 1 to 3 KΩ. There are many things. Transistors 9, 10, 11, 12, 13, and 14 are designed to have a high impedance in the primary winding of this intermediate frequency transformer.
An intermediate frequency transformer 7 with a high frequency conversion gain consisting of
This is to extract a large intermediate frequency signal to 56. Then, the number of secondary windings of the intermediate frequency transformer is reduced to lower the impedance and impedance matching with the filter 65 is performed.

Therefore, an intermediate frequency transformer 66 is required, and the coil A/68 of this intermediate frequency transformer 66 and the capacitor 57 are tuned to the intermediate frequency. Since the value of the capacitor 57 varies, the value of the coil 68 is generally adjusted externally. Therefore, it was necessary to adjust the intermediate frequency transformer 7 when making the receiver.

In view of the above-mentioned problems, the present invention provides a frequency conversion circuit with good performance, in which the filter for extracting the intermediate frequency signal from the output of the frequency conversion circuit is not adjusted.

Means for Solving the Problems In order to solve the above problems, the frequency conversion circuit of the present invention includes first and second transistors whose emitters are connected to each other, and the emitters of the first and second transistors are connected to a second transistor. The fourth and sixth transistors are connected to the collector of the third transistor, and the emitters of the fourth and sixth transistors are connected to the collector of the sixth transistor, and the third and sixth transistors are connected to the collector of the sixth transistor. The emitters of the No. 6 transistors are connected to each other, an input signal or a local oscillation signal is applied to the base of at least one of the third and sixth transistors, and the connection point between the bases of the first and sixth transistors is connected. , a local oscillation signal or an input signal is applied to at least one connection point between the bases of the second and fourth transistors, and a local oscillation signal or an input signal is applied to the connection point between the first and fourth transistors and the second and sixth transistors. Take out two signals of opposite polarity that have been frequency-converted from both connection points of the collectors of The structure is such that this signal is extracted from at least one of the seventh and eighth transistors to an unadjusted intermediate frequency filter via an output circuit with low impedance.

Operation The present invention amplifies two signals of opposite polarity that have been frequency-converted by the above configuration using a differential amplifier to increase the gain.
After that, impedance matching is performed via a low-impedance output circuit to an unadjusted intermediate frequency filter, resulting in good S/N sensitivity, and it is possible to eliminate adjustment by using an intermediate frequency filter such as a ceramic filter. .

Embodiments Hereinafter, frequency conversion circuits according to embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an electrical connection diagram of a frequency conversion circuit in one embodiment of the present invention. In FIG. 1, 1 is a frequency conversion circuit, 2 is an intermediate frequency amplifier, 3 is a detection circuit, and 6
5 r is an antenna coil, 5 r is a hub capacitor, 53 is a local oscillation coil, 56 is an intermediate frequency filter, 4. Completed, 5
1.54 is a capacitor, 8.15, 16, 19, 20,
27, 28, 29° 30.35, 37.40 are resistances, 2
1, 22.23° 26.36.39 is a current source, 9 to 14
+24+25t31 to 34.38 are transistors.

The operation of the frequency conversion circuit configured as described above will be explained using FIG. 1.

Varicon 5. The input signal of the antenna coil/l/6 which constitutes the tuning circuit with the capacitor 4 is applied to the base of one of the transistors 9 and 1o whose emitters are coupled to each other, as well as the collector and the collector of the transistors 9 and 10. and the emitters of transistors 13.14, as well as transistors 24.26 and coils 53. Capacitor 51. The local oscillation signal of the local oscillation circuit composed of the tuning circuit of the variable capacitor 52 switches the signal applied to the base of the transistor 11.14 as well as the emitters of the transistors 11.12 and 13.14 via the resistor 2o. Then, two frequency-converted signals of mutually opposite polarity are taken out at the connection point 85 of the collector of the transistor 11.13 and the connection point 86 of the collector of the transistor 12.14, and are then passed through the capacitor 17.18 to the connection point 86 of the collector of the transistor 12.14. 32 base plus amplification.

A diode-connected transistor 33 (which may be a diode) is connected to the collector of the transistor 31, and a PNP (PNP) transistor 34 collector is connected to the collector of the transistor 32, and the diode or diode-connected transistor 33 and transistor 34 function as a current mirror circuit. The signal that is activated and amplified to the collectors of the transistors 32 and 34 is sent to the base of the emitter follower transistor 38, and then to the intermediate frequency filter (ceramic filter in this case) via the emitter of this transistor 38 and the resistor 40. Extract the frequency signal.

This intermediate frequency signal is amplified by an intermediate frequency amplification circuit 2, and detected by a detection circuit 3 (here, a M detection circuit) to extract a detection output signal. When the detection circuit 3 is an AM detection circuit, a signal whose DC voltage changes depending on the magnitude of the signal level is used as an automatic gain control signal, and is added to the intermediate frequency amplifier 2 at line 72 in FIG. 1 to perform automatic gain control. , 73 to the frequency conversion circuit 1 (bases of transistors 1o, 9) and automatic gain control. When the voltage of this dark line 73 decreases, the currents of the transistors 9 and 1o decrease, thereby controlling the gain.

Here, the value of the load resistance 15.16 of the frequency conversion circuit is lower than the primary side impedance of the conventional intermediate frequency transformer 56 shown in FIG. If this resistance value in Figure 1 is increased to 20 to 30 Ω, the voltage drop will be large.
It cannot be used if the power supply voltage of Vca is low. Therefore, in order to use it at a low voltage, it is necessary to reduce the value of the resistor 15.16. For example, in order to operate with Vcc of 1.6V, the voltage drop across resistor 15.16 should be o,s~0.7
It needs to be in v position. If the current flowing through the resistor 15.16 is 200 .mu.m, the resistance will be 2.5 to 3.6 .OMEGA. Therefore, the conversion gain of the frequency conversion circuit is lower than when using the conventional intermediate frequency transformer 56. Therefore, in the embodiment of the present invention shown in FIG. 1, the two signals of the load resistor 16.16 are applied to the base of the transistor 31.32 via the capacitor 17.18, and are amplified by the differential amplifier transistor 31.32. A signal is taken out to the collectors of transistors 32 and 34. At this time, the reason why both signals of the collector signals of transistors 11.13 and 12.14 of the frequency conversion circuit are applied to both transistors 31.32 of the differential amplifier is to increase the gain. (If only one of these signals is amplified, the gain is small.) If only one signal is amplified by a later amplifier, the gain will increase, but if it is amplified by a later amplifier, it will amplify the noise of the transistor, so the S/ N
The ratio becomes worse. Therefore, in order to increase the gain of the previous stage by using both outputs of the frequency conversion circuit, both of the signals are amplified using a differential amplifier.

Next, if the emitter follower transistor 38 is used,
Since the base in B-Danne of this transistor 38 is high, the gain is almost determined by the load resistor 36 of the differential amplifiers 31 and 32, and a large gain can be obtained. Furthermore, since the impedance of the emitter of the transistor 38 is low, if the impedance of the filter 65 is about 3.OMEGA., impedance matching can be achieved by varnishing the resistor 40 to about 3.times..OMEGA. That is, the emitter follower transistor 38 is used for impedance conversion.

Furthermore, differential amplifiers 31 and 32 and PNP) transistors may be used, but when integrated into an IC, PNP) transistors have a higher MP) ), 7
using a register. And this NPN ) transistor 3
1.32 base voltage and transistors 11, 13, 12
, 14 collector voltages could not be made the same, so capacitor 1 was used.

18 is used.

It is also possible to operate the resistor 30 at the emitter of the transistors 31 and 32 by using a current source using a transistor, but if a transistor is used, the noise of the transistor becomes large, so the resistor 30 at the emitter of the transistor 31 and 32
o is used.

As described above, the two frequency-converted signals of opposite polarity are amplified by a differential amplifier, and the intermediate frequency signal is taken out to a non-adjustable filter such as a low impedance ceramic filter, and the intermediate frequency filter is not adjusted. A frequency conversion circuit with good performance can be constructed.

FIG. 2 shows a frequency conversion circuit showing a second embodiment of the invention. In this figure 2, transistor 9 of the frequency conversion circuit is shown.
, 1o, and if an input signal is applied to one of the bases of transistors 11, 14, 12, and 13, the same operation as in FIG. 1 is achieved.

At this time, automatic gain control is performed by turning on the transistor 96 when a positive voltage is applied to the line 73 and lowering the current of the transistors 9 and 10.

FIG. 3 shows a frequency conversion circuit showing a third embodiment of the present invention. In this figure 3, the current mirror circuit shown in figure 1 is removed from the transistor 31°320 collector, and the resistor 3
5, and operates in the same manner as the embodiment shown in FIG.

FIG. 4 shows a frequency conversion circuit showing a fourth embodiment of the present invention. In the fourth embodiment, the emitter follower transistor 38 shown in FIG. 3 is omitted. This load resistance 3
Impedance matching can be achieved by changing 5 to 3 Ω, which has a low impedance that is almost the same as the resistance shown in FIGS. 1 to 3. However, as shown in Figures 1 to 3, the transistor 3
Although the gain of 1.32 is small, since a differential amplifier is used to amplify the two signals of the frequency conversion circuit, the gain is somewhat large, so the case in Figure 4 is almost the same as the one in Figure 1. can be operated.

Effects of the Invention As described above, the present invention amplifies two signals of opposite phases obtained by converting the frequency of an input signal and a local oscillation signal using a differential amplifier, and then outputs the signals as a low impedance output to an unadjusted intermediate frequency filter. By configuring it to be taken out, S/
It is possible to eliminate intermediate frequency adjustment while maintaining good N sensitivity.

[Brief explanation of drawings]

FIG. 1 is an electrical connection diagram of a frequency conversion circuit according to a first embodiment of the present invention, FIG. 2 is an electrical connection diagram of a frequency conversion circuit according to a second embodiment of the present invention, and FIGS. The figure shows the third aspect of the present invention. An electrical wiring diagram of a frequency conversion circuit showing a fourth embodiment, and FIG. 5 is an electrical wiring diagram of a conventional frequency conversion circuit. 1... Frequency conversion circuit, 2... Intermediate frequency amplifier, 3... Detector, 6... Antenna coil, 5.52...・Variable capacitor, 53...
...Local oscillation coil, 65...Intermediate frequency filter, 56...Intermediate frequency transformer, 9-1
4,24,25.31~34,38°96...
Transistor, 4, 7, 51.54... Capacitor, 8, 15.16, 19, 2Φ, 27° 28.29
, 30, 35, 37, 40, 92°93.94...
...Resistance, 21. 22, 23, 26° 36.39.9
1... Current source.

Claims (1)

[Claims] first and second transistors whose emitters are connected to each other; and fourth and fifth transistors whose emitters are connected to the collector of a third transistor, and whose emitters are connected to each other. , the emitters of the fourth and fifth transistors are connected to the collector of a sixth transistor, the emitters of the third and sixth transistors are connected to each other, and at least one of the third and sixth transistors is connected to the collector of the sixth transistor. An input signal or a local oscillation signal is applied to the base of the transistor, and the local oscillation signal is applied to at least one of the connection point between the bases of the first and fifth transistors and the connection point between the bases of the second and fourth transistors. A signal or an input signal is applied, and the frequency is converted from the connection point between the collectors of the first and fourth transistors and the connection point between the collectors of the second and fifth transistors. A signal is taken out, these two signals are added to the bases of seventh and eighth transistors for a differential amplifier, amplified, and this signal is outputted from at least one of the seventh and eighth transistors with a low impedance. 1. A frequency conversion circuit characterized in that the frequency conversion circuit is configured to extract an intermediate frequency signal to an unadjusted intermediate frequency filter such as a ceramic filter through the circuit.