JPH0258801B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a modulator used in a radio broadcasting device for the purpose of transmitting amplitude modulated (AM) waves.

(Prior technology) Conventionally, class B modulators have often been used as modulators in AM radio broadcasting equipment, but in recent years, PWM (pulse width modulation) methods have also come into widespread use, improving the power efficiency of modulators. are doing. However, the number
To construct a high-voltage, high-power broadcasting machine operating at 10kV, it was necessary to use vacuum tubes. It is well known that the use of vacuum tubes requires significant maintenance costs due to their relatively short lifetimes. In other words, in the case of high-voltage, high-power broadcasting equipment that requires the use of vacuum tubes in the modulated device, it is impossible to create a high-voltage modulator using low-voltage semiconductor elements such as FETs (field-effect transistors). It was possible.

(Problems to be Solved by the Invention and Means for Solving the Problems) The present invention uses a high-voltage, high-power active amplification element that is normally required when the modulated device of an AM broadcasting device is an anode modulation system. Eliminates the need for long-life
The objective is to provide a modulator with even higher power efficiency using FETs. This method is particularly effective when the modulated device requires high voltage.

(Configuration of the Invention) FIG. 1 is a diagram showing an example of the configuration of a modulator according to the present invention. The audio signal AF superimposed on V 1 with the V ₁ reference voltage is applied to the A/D converter ₁ , and its digital output is decoded by the decoder 2 and then
Given to gate 3. In addition to this, a signal from a sampling frequency generator 5 is input to the AND gate 3, and switching is repeated. Decoder 2
Of the output signals C ₁ to _{C 31} , switching waveforms appear in the outputs of some AND gates for lines with outputs, and the signals are output via the pulse driver 4.
Switch the appropriate one among FETQ ₁ to Q ₃₁ . When FETQ ₁ to Q ₃₁ have a switching input, a rectangular wave current flows through the corresponding one of transformers T ₁ to _{T 31} , and a rectangular wave is also generated on the secondary side of the transformer. This rectangular wave is rectified by diodes _D1 to _D31 , respectively. In this figure, D ₁ to _{D 31} are configured as full-wave rectifier circuits, but there is no need to be limited to this, and any configuration may be used as long as the rectified voltages of the outputs of T ₁ to _{T 31} are added. This added voltage appears at point α in the figure and passes through a low frequency filter (LPF) consisting of L ₁ and C ₁ to provide a modulator output at point e.

(Operation of the Invention) First, the case where there is no voice input AF in FIG. 1 will be explained. If there is no input AF, the voltage at the input a of the A/D converter will be only the voltage of the reference power supply _V1 for determining the modulator output voltage when only the carrier wave is present.
The output of the A/D converter 1 is a binary code, and in this example, since it has a resolution of 5 bits, it can be resolved into 1/32. That is, for ease of understanding, if it is set to 15 when there is only a carrier wave, the output of the A/D converter 1 is only b ₁ , b ₂ , b ₃ , and b ₄ and no output is output to b ₅ . This is decoded by the decoder 2. The decoder 2 converts a 5-bit binary code input into 32 (0 to 31) steps, and outputs appear at _C1 to _C15 when there is only a carrier wave.
This output is given to AND gates _G1 to _G15 .
These AND gates are switched by a rectangular wave of about 100kHz from the sampling frequency generator 5, so the output of the decoder 2 is present.
A rectangular wave signal appears on the output side of the gate, and FETQ ₁ to Q ₁₅ are repeatedly turned on and off through the pulse driver 4.

Now, if we focus on the on/off of only Q ₁ , it is 1 of T ₁ .
A switching current due to _Q1 flows in the next coil,
A voltage proportional to the turns ratio appears in the secondary coil. Since rectifiers D ₁ to D ₃₁ are connected in series
The output voltage rectified by D ₁ passes through D ₂ to D ₃₁
Appears at the output e of the LPF. When transmitting a carrier wave, Q ₁ ~
Since _Q15 is repeatedly turned on and off, a stack of voltages rectified by _D1 to _D15 appears at the output e.

Next, the case where the audio signal AF is input will be explained. Now, when a signal like the one from point A to point B in Figure 3 is input to A/D converter 1, its output b ₁
~ _b5 changes moment by moment according to the input level. Note that the A/D converter 1 and the decoder 2 perform data conversion and data latching at a sufficiently high clock frequency (several MHz), and since these operations are well known, their explanation will be omitted.

Now, the input level of the audio input signal changes b ₁ to _{b 5}
When C changes according to its level, C ₁ to C ₃₁ also change. If there is a signal in all C ₁ ~ _{C 31} then Q ₁ ~
Q ₃₁ all switching, transformer T ₁ ~ _{T 31}
Switching drives everything. Clearly this condition is the maximum output of this modulator. Further, when the voltage at point a becomes zero due to a change in the audio signal, there is no signal at all C ₁ to _{C 31} and all FETs Q ₁ to _{Q 31} stop switching. This state is the lowest output of this modulator, which is zero volts.

In this way, when audio is input centered around the carrier wave level, the output of the modulator changes according to the audio, and the modulated device can be driven. in this circuit
The operation of FETQ ₁ to _{Q 31} is a switching operation, so the power efficiency is extremely high, reaching approximately 90%.

Here, FIGS. 2 and 3 will be explained. Second
The figure shows the waveforms of the total current flowing through the transformers T ₁ to T ₃₁ and the voltage at point d in Figure 1. The former is a rectangular wave, and the latter is the sum of the rectified voltages of the diodes D ₁ to _{D 31} , which is a step-like waveform. It is a waveform.

Figure 3 shows the waveform at the input point a in Figure 1, and
It is also the waveform of the output e of the LPF (L ₁ and C ₁ ), that is, the modulator output voltage, and the sampling frequency is approximately
This is a waveform with 100kHz and its harmonic components removed.

In the above example, a 5-bit A/D converter is used to construct a modulator with a 1/32 step-like waveform, but it is clear that the higher the resolving power, the more faithful the waveform output can be obtained. Bit's A/
If a D converter is used, it becomes a 1/64 step waveform, which doubles the resolution and improves the waveform.
However, this is determined by economic constraints.
Increasing the resolution increases the required number of FETs, transformers, diodes, etc., but the transformer T in particular is used for high voltage,
Since it is a modulator for high power use, it requires a high-voltage modulator and is expensive, which has a significant impact on economic efficiency.

(Effects of the invention) By implementing the present invention, a modulator that requires high power and high voltage output uses a long-life FET and a diode rectifier that can easily achieve long life and high voltage resistance, instead of using a short-life vacuum tube. What can be achieved by
FETs have significant advantages over conventional FETs, such as a semi-permanent life, significantly reduced maintenance costs, and high power efficiency due to switching operation.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of a modulator according to the present invention, and FIG.
The figure is a waveform diagram of the total current flowing through the transformer in FIG. 1 and the current at point d, and FIG. 3 is a waveform diagram of the input point a and the output point e in FIG. 1...A/D converter, 2...decoder, 3
...AND gate, 4...Pulse driver, 5...
...Sampling frequency generator, Q...FFT (field effect transistor), T...Transformer, D...Diode rectifier, _V1 ...Reference voltage.

Claims (1)

[Claims] 1. An input audio signal is input to an A/D converter and decoder circuit together with a reference voltage that sets the level of the carrier wave, and is digitized step by step. The digital signal obtained at each step according to the level of the input signal is converted into a sampling pulse. and amplifying each of the switching semiconductor elements in each of the stages to which the primary winding of a transformer having a DC-insulated secondary winding is connected as an output load. 1. A high-efficiency AM modulator, characterized in that a voltage obtained by rectifying the secondary output of a transformer of each switching semiconductor element and adding the voltage in the order of the steps is passed through a low frequency generator and used as a modulator output.