RU2252482C1 - Pulse modulator - Google Patents

Abstract

FIELD: radio engineering and measurement technology.

SUBSTANCE: proposed pulse modulator has two diodes, two isolating capacitors, bipolar current supply controlled by modulating signal, load resistor relative to common conductor, and line transformer incorporating two windings cumulatively connected in series.

EFFECT: enlarged range of modulated frequencies.

1 cl, 1 dwg

Description

The invention relates to radio engineering and can be used in measuring technique, where it is required to obtain radio pulses in a wide range of modulated frequencies.

Known pulse modulator described in the article by A.G. Samoilova, S.A. Samoilova, P.A. Semushina “Powerful high-frequency transistor generators”, magazine “Instruments and experimental equipment”, 1996, No. 6, containing a series-parallel switch on two diodes. A high-frequency modulated signal is supplied to the first input of the modulator, through an isolation capacitor, and a modulating signal from the control circuit via a decoupling high-frequency inductor is fed to the second input.

The use of a high-frequency inductor, which always has an inter-turn capacitance for supplying the modulating signal, leads to resonance phenomena and a narrowing of the range of modulated frequencies.

Also known is a pulse modulator used in a high-frequency signal generator G4-151 (see Technical description and operating instructions for a high-frequency signal generator G4-151, clause 4.2.5), containing two isolation capacitors, two diodes, the anode of the first diode connected to the cathode of the second, the anode of the second is connected to a common conductor, and a bipolar current source controlled by a modulating signal is connected to a common point of connection of the diodes. The modulated signal is fed to the first input of the modulator through a U-shaped LC high-pass filter, and the modulating signal is fed to the second input from a controlled bipolar current source and is closed to a common conductor through the inductance of the U-shaped LC high-pass filter, which has a low resistance for modulating signal.

The disadvantage of this device is the narrow range of modulated frequencies, since when expanding the range down in frequency, the nominal value of the inductances of the LC filter and, therefore, the inter-turn capacitance of the inductors increases, which limits the frequency range from above.

The purpose of the invention is the expansion of the range of modulated frequencies.

The goal is achieved due to the fact that in the pulse modulator containing two isolation capacitors, two diodes, the anode of the first diode connected to the cathode of the second, the anode of the second connected to a common conductor, and a bipolar current source controlled by a modulating signal connected to a common point of connection of the diodes, and, through the second isolation capacitor, the load resistance relative to the common conductor, an additional transformer is introduced on the line with two windings connected in series according to the windings, with the beginning of the first the windings are connected through the first isolation capacitor to the source of the modulated signal, and the end of the second winding is connected to a common conductor, the common connection point of the windings is connected to the cathode of the first diode.

The drawing shows a block diagram of a pulse modulator.

The drawing shows:

1, 2 - the first and second isolation capacitors, respectively;

3 - transformer on the line;

4, 5 - the first and second diodes, respectively;

6 - load resistance;

7 - source of bipolar current.

The proposed pulse modulator contains the first and second isolation capacitors 1 and 2, a transformer 3 on the line, the first and second diodes 4 and 5, the load resistance 6, a bipolar current source 7, controlled by a pulse modulating signal.

The pulse modulator operates as follows. The modulated high-frequency signal through the isolation capacitor 1 and then through the transformer on line 3 is fed to the first input of the key, made on diodes 4 and 5. The modulating signal is fed to the second input of the key from the source of bipolar current 7, controlled by modulating pulses. The positive current of the controlled source of bipolar current 7 opens the diode 4 and closes to a common conductor through the second transformer winding on line 3, which has a low resistance for the modulating signal. A positive voltage on diode 4, which is formed when a current flows through it, closes diode 5. Through an open diode 4 and an isolation capacitor 2, a modulated signal is supplied to the load resistance 6. A negative current of a controlled source of bipolar current 7 opens diode 5. A negative voltage generated during current flow on the diode 5 closes the diode 4, and the high-frequency signal to the load resistance 6 does not pass. As a result of this, a high-frequency signal is modulated in amplitude by modulating pulses.

The transformer on the line is a broadband device, its operating frequency range reaches ten octaves with a load resistance of ≤500 Ohms.

Thus, the introduction of a transformer on the line allows you to expand the range of modulated frequencies of the pulse modulator due to the large broadband of the transformer on the line and apply to the diode key through the second winding of the transformer a relatively low-frequency modulating pulse signal, since the winding represents a low resistance for it.

As elements for implementing a pulse modulator, you can use: switching diodes 2A566A-3, isolation capacitors K10-17v, a transformer on the line can contain 7 turns of cable RD 100-1-21 on a ferrite core of grade M1000NN18 of size K7 × 4 × 2, load resistance 50 ohms.

For better coordination with the load, the modulated signal must be supplied from a current source with an output impedance of 200 Ohms.

To obtain a large suppression of the modulated signal in a pause (75 dB in static mode at frequencies up to 200 MHz) and to reduce the penetration of the modulating signal into the load, two such modulators can be connected in series, and the second modulator is connected by the transformer to the load, forming a symmetrical circuit. In this case, a load with a resistance of 50 Ω can be connected to the modulator through an emitter follower with an input resistance of 200 Ω and an output of 50 Ω. The voltage transfer coefficient of such a matching stage is about unity.

Claims (1)

A pulse modulator containing two isolation capacitors, two diodes, the anode of the first diode connected to the cathode of the second, the anode of the second connected to a common conductor, and a bipolar current source controlled by a modulating signal connected to the common point of the connection of the diodes, and the load resistance relative to a common conductor, characterized in that a transformer is inserted into it on a line with two windings connected in series according to one another, the beginning of the first winding being connected through of the first capacitor to the source of the modulated signal and the end of the second coil is connected to a common conductor, a common connection point of the windings connected to the cathode of the first diode.