JP2888880B2 - Balanced modulation circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a balanced modulation circuit used for an RF modulator or the like.

FIG. 2 is a circuit diagram showing a configuration of a conventional balanced modulation circuit. The carrier signal output from the carrier oscillator 1 is supplied to the primary coil 14a of the transformer 14. The secondary coil 14b of the transformer 14 has its midpoint grounded via a capacitor 15, and the carrier signal is converted into a balanced signal and output from the secondary coil 14b. FIG. 3 shows the actual configuration of the transformer 14, and portions corresponding to those in FIG. 2 are denoted by the same reference numerals. As shown in FIG. 3, a primary coil 14a is realized by a rod-shaped conductive path for propagating a carrier signal output from the carrier oscillator 1, and a secondary coil is formed by a pickup loop disposed opposite to the rod-shaped conductive path. 14b has been realized.

In FIG. 2, the secondary coil 14b has one end connected to the anode of the balance modulation diode 9 and the other end connected to the cathode of the balance modulation diode 10. The cathode of the diode 9 and the anode of the diode 10 are connected to the output terminal 13 together with the other end of the resistor 11 whose one end is connected to the input terminal 12. Here, a video circuit is connected to the input terminal 12. The resistor 11 is a matching resistor provided for matching with the output impedance of the video circuit. According to this balanced modulation circuit, the carrier signal output from the carrier oscillator 1 is balanced-modulated by the video signal input to the input terminal 12 and output from the output terminal 13.

[Problem to be Solved by the Invention] By the way, in the above-mentioned conventional balanced modulator, since the middle point of the secondary coil 14b is grounded via the capacitor 15, the output is applied to both ends of the secondary coil 14b. If the primary coil 14a and the secondary coil 14b are not fixed in an optimal positional relationship at the time of manufacture, or if the characteristics of the diode 9 and the diode 10 vary, In some cases, or when the wiring pattern of the circuit is asymmetric, modulation is performed in an unbalanced state, causing distortion in the modulated wave signal. For this reason, conventionally, after manufacturing, the distance between the primary coil 14a at both ends of the secondary coil 14b is changed, or the secondary coil 14b is connected to the primary coil 14b as shown by broken lines U and V in FIG. Adjust the position of the secondary coil 14b by tilting it with respect to the secondary coil 14a to obtain the maximum degree of modulation, and fix the secondary coil 14b when the position adjustment is completed. I was By adjusting the degree of modulation to be the maximum, distortion of the modulated wave signal can be minimized. However, this adjustment work is extremely difficult and troublesome. Further, after the adjustment, there is a problem that the secondary coil 14b may be shifted from the adjustment position due to external vibrations or the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a balanced modulation circuit having less distortion and requiring no adjustment work after manufacturing.

[Means for Solving the Problems] The present invention provides a transformer that receives an output signal on a primary side from a carrier oscillator and has no secondary center, and each emitter is grounded via a common constant current circuit. A differential amplifier that differentially amplifies the secondary side output of the transformer and outputs balanced signals of opposite phases to each other, and one of the pair of amplifiers A first diode whose output terminal is connected to the anode, and a second diode whose output terminal of the other amplifier is connected to the cathode, wherein the cathode of the first diode and the second diode are connected. An anode is connected, a modulation signal is input to the connection point via a resistor, and a modulated signal is output from the connection point.

[Operation] According to the above configuration, a signal corresponding to the oscillation output of the carrier oscillator is output to the secondary side of the transformer. The output of the secondary side of the transformer is differentially amplified by the differential amplifier to generate balanced signals having phases opposite to each other, and these balanced signals are modulated by the input signal and output.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of a balanced modulation circuit according to one embodiment of the present invention. In this balanced modulation circuit, a transformer 2 having a fixed relative position between a primary coil and a secondary coil is used in place of the transformer 14 in FIG.
Both ends of the secondary coil of the transformer 2 are input to the bases of the transistors 3 and 4, respectively. The collectors of the transistors 3 and 4 are connected to a power supply terminal 5 via current limiting resistors 6 and 7, respectively, and the emitters of the transistors 3 and 4 are connected to a constant current source 8 having one end grounded. Commonly connected to the other end. The collector of the transistor 3 is connected to the anode of the diode 9, and the collector of the transistor 4 is connected to the cathode of the diode 10. The other configuration is the same as the configuration in FIG. 2 described above.
Corresponding parts have the same reference characters allotted, and description thereof will not be repeated.

In this balanced modulation circuit, an output signal corresponding to the carrier signal is obtained from the secondary side of the transformer 2. The secondary output of the transformer 2 is composed of transistors 3 and 4, a constant current source 8,
The signal is differentially amplified by a differential amplifier circuit including resistors 6 and 7. As a result, regardless of the positional relationship of the secondary coil of the transformer 2 with respect to the primary coil, as shown in FIG. , The secondary side of the transformer 2 does not need to balance the carrier signal output to both ends. Therefore, the adjustment positions of the primary side coil and the secondary side coil of the transformer 2 become irrelevant, and a current loop is formed in which the current flows into the constant current source 8, and balanced signals of opposite phases are generated by the collectors of the transistors 3 and 4. Generated from.

While the video signal input to the input terminal 12 is positive, the diode 9 is turned off. During this period, when the output of the secondary side of the transformer 2 becomes the polarity shown by the arrow A and the collector of the transistor 4 becomes L level, the diode 10 turns on and the modulated wave signal becomes the clamp level. When the output of the secondary side of the transformer 2 is inverted to the polarity shown by the arrow B, the diode 10 is turned off, and the video signal is output as a modulated wave signal. Similarly, when the video signal is negative, the diode 10 is turned off, and the diode 9 is turned on / off in response to the polarity of the secondary output of the transformer 2 switching to A / B. . In this way, the balanced signals having mutually opposite phases are modulated by the video signal and output to the output terminal 13.

[Effects of the Invention] As described above, according to the present invention, there is an effect that a balanced modulation circuit that does not cause modulation distortion and that does not require adjustment after manufacturing can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a configuration of a balanced modulation circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a configuration of a conventional balanced modulation circuit, and FIG. FIG. 9 is a diagram illustrating an adjustment operation after manufacturing in the balanced modulation circuit. 3, 4 transistors, 8 constant current sources, 2 transformers, 1 carrier oscillator.

Claims (1)

(57) [Claims] 1. A pair of transformers having a secondary side receiving a carrier wave oscillator output signal on a primary side and having no middle point on a secondary side, and a pair of transistors each having an emitter grounded via a common constant current circuit. An amplifier having a differential amplifier for differentially amplifying a secondary output of the transformer and outputting balanced signals having phases opposite to each other; and an output terminal of one of the pair of amplifiers is connected to an anode. And a second diode having an output terminal of the other amplifier connected to the cathode, wherein the cathode of the first diode and the anode of the second diode are connected, and A modulated signal is input to a point via a resistor, and a modulated signal is output from the connection point.