JPS6034295B2 - frequency conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency conversion circuit used in radio receivers, etc., which prevents the output of a local oscillation circuit from leaking to an intermediate frequency stage as much as possible, and has a simple configuration and excellent conversion efficiency. The purpose of this invention is to provide a frequency conversion circuit that has the following characteristics.

Generally, a frequency conversion circuit is configured to apply a high frequency signal to the base of a frequency conversion transistor, apply the output of a local oscillation circuit to the emitter, and extract from the collector an intermediate frequency signal with a frequency equal to the difference between the two.

However, this type of frequency conversion circuit that has been used in the past is configured with one transistor for frequency conversion, which is not very desirable because the output of the local oscillation circuit may leak to the collector. The present invention eliminates the above-mentioned drawbacks of the conventional structure, and uses one more transistor in addition to the frequency conversion transistor, and connects the collectors of the two transistors to the output of the local oscillation circuit. The structure is such that the leakage components that appear cancel each other out.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The frequency conversion circuit of 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 frequency conversion circuit of the present invention, in which 1 is a high frequency circuit, 2 is a frequency conversion circuit, and 3 is a local oscillation circuit.

and 11 is a coupling capacitor for guiding the output of the high frequency circuit 1 to the base of the frequency conversion transistor 14; 12, 13;
is a base bias resistor of the frequency conversion transistor 14, 15 is a separately provided transistor, 16 and 17 are emitter resistors of the transistors 14 and 15, and 18 and 19 are used to connect the output of the local oscillation circuit 3 to the emitters of the transistors 14 and 15. Coupling capacitor 20' leading to transistor 1
An intermediate frequency transformer connected between collectors 4 and 15.
21 and 22 are resistors for base bias of the transistor 15, and 23 and 24 are compensation resistors and capacitors for making the base impedance of the transistor 15 equal to the base impedance of the transistor 4. In the above embodiment, the output of the high frequency circuit 1 is applied to the base of the frequency conversion transistor 14 via the capacitor 11, the base signal of the transistor 4 is output to the emitter of the transistor 4,
? 19 to the emitter of transistor 15.

Then, the output of the local oscillation circuit 3 is connected to capacitors 18 and 19.
is applied to the emitters of transistors 14 and 15 via. Therefore, an output corresponding to the difference between the input signal and the local oscillation signal appears at the collectors of the transistors 14 and 15, and a frequency-converted intermediate frequency signal appears at the output end of the intermediate frequency transformer 20. In this case, the output of the local oscillation circuit 3 leaks to the collector side of the transistor 14 as in the conventional case, but according to the above embodiment, the output of the local oscillation circuit 3 leaks to the collector side of the transistor 14.
The output of is applied not only to the emitter of the frequency conversion transistor 4 via the capacitor 18, but also to the emitter of the separately provided transistor 15 via the capacitor 19. The output of the local oscillation circuit 3 appears at the collectors of both transistors 4 and 15, so the outputs of the local oscillation circuit 3 appearing at the collectors of both transistors 4 and 15 cancel each other out through the intermediate frequency transformer 20, and the output of the intermediate frequency transformer 20 At the end, the output of the local oscillation circuit 3 hardly appears.
That is, according to the above embodiment, the transistors 14,1
The outputs of the local oscillation circuit 3 appear in the same phase, but these outputs have opposite phases at points a and b due to the primary winding of the intermediate frequency transformer 20, so they cancel each other out. and does not appear at the output end of the intermediate frequency transformer 20 at all. In this case, it is desirable that the primary winding of the intermediate frequency transformer 20 be grounded at its midpoint, and that the amplification degrees of the transistors 14 and 15 be the same.

Therefore, in the above embodiment, a series circuit of a resistor 23 and a capacitor 24 is connected between the base of the transistor 15 and the ground, so that the base impedance of the transistor 15 is made equal to the base impedance of the transistor 14. . In this way, according to the above embodiment, one more transistor is provided in addition to the frequency conversion transistor, and the output of the local oscillation circuit is applied to the emitters of these two transistors, and the output is applied to the collector of the frequency conversion transistor. The output of the local oscillation circuit described above is canceled out by the output appearing at the collector of another transistor, and the output of the local oscillation circuit leaking to the output terminal of the intermediate frequency transformer can be minimized. It is possible.

In the embodiment, a series circuit consisting of a resistor 23 and a capacitor 24 is connected between the base of the transistor 5 and the ground so that the base impedances of the transistors 14 and 15 are equal to each other.
It is not necessarily necessary to connect a series circuit consisting of a resistor 23 and a capacitor 24 between the base of the resistor 23 and the ground.

In other words, even if the primary winding of the intermediate frequency transformer 20 is grounded at its midpoint, the base bias resistor 21,
It is also possible to make the amplification degree equal to 22.
Further, in the above embodiment, a capacitor is connected in parallel to the primary winding of the intermediate frequency transformer 20, but a capacitor may be connected in parallel to the secondary winding as shown in FIG. As is clear from the above embodiments, the present invention has a first transistor for frequency conversion to which an input signal is applied to the base, and another second transistor in addition to this first transistor. An intermediate frequency transformer whose middle point is grounded is connected between the collectors of the first and second transistors, and the emitters of the first and second transistors are coupled to each other in an alternating current manner. The output signals of the local oscillation circuits are applied to the respective emitters, and the base impedances of the first transistor and the second transistor are approximately equal, so that the first and second transistors operate differentially. , the intermediate frequency signal which is the difference signal between the input signal and the local oscillation signal is the first
, they become mutually opposite phase signals at the collector of the second transistor, and these opposite phase signals are added by an intermediate frequency transformer whose middle point of the primary winding is grounded, allowing a large output to be taken out to the secondary winding. , the local oscillation signal is an in-phase signal at the collectors of the first and second transistors, and is canceled by the intermediate frequency transformer.

Therefore, according to the present invention, leakage of local oscillation output can be almost completely prevented, and frequency conversion efficiency can be significantly improved. Therefore, the frequency conversion circuit of the present invention is particularly effective as a first frequency conversion circuit of the double superheterodyne system. In other words, if there is a leakage of local oscillation output in a duffle superheterodyne receiver, a second intermediate frequency signal may appear due to the leakage even in a non-receiving state, and the receiver may operate as if it were in a receiving state. According to the present invention, there is almost no leakage of local oscillation output, so
There are almost no such problems and it is extremely advantageous.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electrical wiring diagram of one embodiment of the frequency conversion circuit of the present invention, and FIG. 2 is an electrical wiring diagram of main parts of another embodiment. DESCRIPTION OF SYMBOLS 1... High frequency circuit, 2... Frequency conversion circuit, 3... Local oscillation circuit, 14... Frequency conversion transistor, 15... Transistor, 20...
...Intermediate frequency transformer, 23, 24...Resistor, capacitor. Figure 1 Figure 2

Claims (1)

[Claims] 1. A first base for frequency conversion to which an input signal is applied.
A transistor, and a second transistor in addition to the first transistor, an intermediate frequency transformer having a primary winding whose midpoint is grounded is connected between the collectors of the first and second transistors, and The emitters of the first and second transistors are coupled to each other in an alternating current manner, and
, the output signal of the local oscillation circuit is applied to the emitter of the second transistor, and the base impedance of the first transistor for frequency conversion and the other second transistor are applied.
A frequency conversion circuit configured so that the base impedances of the transistors are almost equal to each other. 2. The frequency according to claim 1, characterized in that a series circuit consisting of a resistor and a capacitor is connected between the base of another second transistor provided in addition to the first transistor for frequency conversion and the ground. conversion circuit.