JPH028425Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field This invention relates to a frequency conversion circuit, particularly a double-balanced mixer suitable for frequency processing of wideband signals in CATV converters and the like.

BACKGROUND ART CATV receiving tuners and converters use double-balanced diode mixers that have low loss over a wide dynamic range and excellent isolation characteristics between input and output. As shown in Figure 1, the basic circuit of this double balanced diode mixer consists of a balanced transformer coil 4 connected between a local injection port 1 for local oscillation signals, an RF input port 2 for received signals, and an IF output port 3 for intermediate frequency signals. ~7 and diode 8
.about.11, and is used in VHF band wideband tuners, etc., as it sufficiently reduces leakage of local oscillation voltage and is effective in intermodulation interference. The specific mixer circuit is as shown in Figure 2.
An input transformer T 1 and an output transformer T ₂ are inserted on the RF input port ₂ and IF output port 3 sides, and the same diodes 8 to 11, balance coils 13 to 16, and capacitors 17 to 17 as shown in FIG. 1 are connected between each port. 2
2, further coupled by a bypass capacitor 23
and a load resistance 24 in parallel circuit stability control circuit 27
It is constructed with attached. In this balance mixer circuit, when looking at the output side from the balance coil 14 of the balance transformer, the left and right sides must be perfectly balanced, and if this balance is lost, the intended purpose will not be achieved. . Since it is usually installed using printed wiring, it is difficult to arrange the wiring pattern shape and the distance between parts symmetrically, and it is difficult to achieve perfect balance due to the effects of strain capacitance and lead inductance, as well as variations between the parts used. Katta. Here, the load resistor 24 of the stability control circuit 27 is balanced by providing a test point 26 on the load resistor 24 in order to increase the DC stability of the diode by its resistance value, and measuring the potential here and checking the circuit operating current. The stable condition was confirmed. However, the degree of balance, which is an important characteristic of a double-balanced mixer, cannot be confirmed with such a circuit, and it has not been possible to improve the degree of balance by replacing parts or changing the wiring state.

DISCLOSURE OF THE INVENTION Therefore, the present invention has been proposed in view of the above, and aims to provide a new and improved double-balanced mixer that allows the balance of the circuit configuration to be confirmed.

According to the present invention, it has an RF input port, a local injection port, and an IF output port, and a balance coil and mixer diode are coupled between them, and a control circuit for stabilizing diode operation consisting of a bypass capacitor and a load resistor connected in parallel is attached. In the frequency conversion circuit, a double balance mixer is disclosed in which the control circuit is divided and arranged for each balance coil. Here, each separate control circuit corresponds to the left and right balance coils, and the test points make it possible to check the left and right stability and the left and right balance state. That is,
Separate stability control circuits ensure the equilibrium of the balanced state, thereby providing an approach to providing a perfectly balanced left-right mixer. Further, the divided arrangement of the load resistors of the present invention, which has the purpose of checking the balance, is practical because it enables correction to an appropriate balanced state by measuring the potential difference between the test points of each load resistor.

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 3 shows a double balance mixer according to the invention. This circuit is completely the same as the conventional circuit shown in FIG. 2, except for the stability control circuit, and the same parts are designated by the same reference numerals and detailed explanations thereof will be omitted. The feature of this invention is that the balance coil 1
Bypass capacitor 3 for each of 5 and 16
Control circuits 35 and 36 are provided, each consisting of a parallel circuit of 1 and 32 and load resistors 33 and 34, and test points 37 and 38 are provided respectively. That is, the degree of balance between the left and right balance coils can be confirmed by the potential difference between the test points 37 and 38, thereby making it possible to obtain the completeness of the left and right balance by replacing circuit parts or modifying the wiring.

Such a double balance mixer is
It is used in the first mixer stage of down dual conversion type CATV converters, achieving low loss and high input/output isolation over a wide dynamic range. In other words, a practical circuit has been provided that makes it possible to stabilize the diode operating current and check the balance in order to bring out the original characteristics of the double-balanced mixer.

[Brief explanation of the drawing]

Figure 1 is the basic circuit diagram of a double balanced mixer.
FIG. 2 is a known practical circuit diagram, and FIG. 3 is a specific circuit diagram of a double-balanced mixer according to the present invention. 1... Local injection port, 2... RF input port, 3... IF output port, 8 to 11... Diode, 15, 16... Balance coil, 31,
32... Bypass capacitor, 33, 34... Load resistor, 35, 36... Control circuit, 37, 38...
...Test point.

Claims (1)

[Claims for Utility Model Registration] Mixer diodes are connected in a bridge shape, and an RF input port and a local injection port are provided at one opposing first vertex via a balance coil.
In a double balanced mixer in which an IF output port is provided at the other opposing second vertex via a balance coil, parallel connection is made to a pair of balance coils on the IF output port side that are split and arranged at the opposite second vertex. A double-balanced mixer characterized by having separate control circuits including bypass capacitors and load resistors.