JPH0148687B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high efficiency linear amplifier suitable for SSB (single sideband) transmitters that require linear power amplification.

Now, broadcasters using pulse width modulation (hereinafter abbreviated as PWM) and amplitude modulation (hereinafter abbreviated as AM) have already been put into practical use and are mainly used for medium wave radio broadcasting. This pulse width modulation method has traditionally been used only for DSB (double sideband) broadcasting.
It is well known that in DSB broadcasting, the carrier wave is always present and is only AMed with audio, but in the case of SSB broadcasting, the carrier wave is reduced or removed, and one side of the sideband is completely removed. There is. In an SSB transmitter, the SSB wave is usually generated in the low-level stage, and the waves are sequentially increased with good linearity, but the problem is that the power efficiency is poor, so for example, it is difficult to integrate the transmitter into an integrated circuit. However, it had the disadvantage that it was difficult to increase its maximum output as explained below. The present invention has been made to solve this problem.

First, in conventional SSB transmitters, SSB waves are amplified using class B or class AB amplification.
FIG. 1 shows an example of the configuration of a conventional SSB transmitter, using an ordinary linear amplifier. In Figure 1
AF is a low frequency input signal, 1 is an SSB generation circuit, 2 is a balanced modulator, f _s1 and f _s2 are carrier frequency inputs, 3 is a bandpass filter, 4 is a preamplifier, and Q ₁ and Q ₂ are power amplifiers. A field effect transistor (FET) is formed, 5 is a matching circuit, and Z _p is an antenna load impedance. To perform linear amplification with this power amplifier circuit, bias is applied to the center c on the gate side.
A certain amount of idle current must flow through FETs Q ₁ and Q ₂ even when there is no signal. The larger this current is, the more linear the output can be obtained, but on the other hand, this current reduces the power efficiency of the power amplifier, Q ₁ ,
_Q2 fever increases. Normally, when a small amount of idle current flows in class B amplification, the power efficiency is in the 40% range, but if you use it to improve the distortion rate and approach class A amplification, the power efficiency will drop to the 30% range. In other words, the power loss will be close to 70%, and the cooling devices for Q ₁ and Q ₂ will also be large.

In the present invention, class D amplification (switching amplification) is used instead of conventional class B or A amplification to linearly amplify signals, increase power efficiency, reduce the number of amplification elements used, and downsize the cooling device. It is characterized by what it can do.

FIG. 2 is a diagram showing an example of the configuration of an SSB transmitter embodying the present invention. 6 in the figure is an SSB generation circuit, which performs balanced modulation of the audio frequency AF using the carrier frequency f _c , and generates SSB from which the f _c component and one sideband, in this example, the lower sideband (or upper sideband) have been removed. obtain. By the way, an SSB signal created from an audio signal has a waveform that is completely different from the original audio signal. Suppose that an SSB wave as shown in Fig. 3 is obtained.
The original audio signal cannot be obtained from this SSB wave simply by envelope detection; normally, the audio signal can only be obtained by combining the SSB signal and carrier component and then performing envelope detection. Are known. In the circuit of the present invention, the SSB wave is first envelope-detected as it is, and the assigned frequency f _s wave is phase-modulated by this detected waveform (the SSB wave is passed through the limiting amplifier 13 and the phase modulation remains, but it becomes a constant amplitude wave). (after amplifying the signal and then using it as a carrier wave) is amplitude-modulated and transmitted as a normal SSB wave. Fig. 2 will be explained below. FIG. 4 is a waveform diagram after envelope detection of the SSB wave in FIG. 3, which corresponds to the f input in FIG. 2.

Returning to Figure 2, 7 is a level shift circuit, 8 is 3
Square wave generator, 9 is a comparator, 10 is a pulse amplifier, 11 is a low pass filter (LPF), 12 is a band pass filter (BPF), 13 is a limiting amplifier, 14 is a pre-stage amplifier, Q ₁ to Q ₄ are switching power amplifiers _Q5 is a switching FET,
T1 is the output transformer. Now, the level shift circuit 7 shifts the pulse width of the output P of the comparator 9 which compares and outputs the signal B from the triangular wave generator 8 and the envelope detection signal A when the envelope detection signal is at zero level as shown in FIG. It is adjusted to zero by h. The pulse P modulated in pulse width by the comparator 9 is shown in Fig. 5, but this figure is an enlarged version of the waveform from a to b in Fig. 4 for ease of understanding, and the sampling frequency is usually around 100kHz. This shows how the waveform of the triangular wave B is compared and pulse width modulated, and the PWM wave P is obtained in this way. This pulse P is amplified by a pulse amplifier 10 and applied to the gate of FET _Q5 .
Therefore, _Q5 performs an on/off operation according to the pulse signal P. It is obvious that the power loss due to the on/off operation of _Q5 is much smaller than when it operates in the active region. Turn on power g by Q ₅ ,
The sampling frequency component of the turned-off power is removed by the LPF 11, resulting in the original envelope waveform, which is applied to _Q1 to _Q4 as modulated power.

On the other hand, the signal of assigned frequency f _s outputted from the SSB generation circuit 6 and subjected to phase modulation passes through the limiting amplifier 13, is amplified by the front stage amplifier 14, and is sent to the transformer T2,
Due to T3, the phase relationship as shown in the figure (Q ₁ and Q ₃ are 180°,
Q ₁ to Q ₄ are switched at a phase difference of 180 degrees between Q ₂ and Q ₄ , and a phase difference of 180 degrees between Q ₁ and Q ₂ . _Q1 ～
Q ₄ forms a class D amplifier, for example Q ₁ and
When Q ₄ is on, Q ₃ and Q ₂ are off, and Q ₃ and Q ₂
When is on, _Q1 and _Q4 are off and alternately turn on and off according to the assigned frequency fs. Since a current whose polarity is reversed as _Q1 to _Q4 are turned on and off flows through the primary side of the transformer T1, this combined induced current flows through the secondary side of T1. Since this current has a switched waveform, unnecessary components are removed by the bandpass filter 12, and the original SSB shown in Figure 3 is applied to the load _Zp such as the antenna.
Power is supplied with an envelope similar to a wave.

Above we have described a circuit that concretely performs power amplification of SSB waves, which particularly require linearity, using class D amplification, but actual measurements have confirmed that the power efficiency can be increased to nearly 80%. As a highly efficient linear amplifier, it is extremely effective in reducing the size of transmitters.

[Brief explanation of drawings]

Figure 1 is an example of the configuration of a conventional SSB transmitter, Figure 2 is an example of the configuration of an SSB transmitter implementing the present invention, and Figure 3 is an example of the configuration of an SSB transmitter according to the present invention.
The figure is an example of an SSB wave, Figure 4 is a waveform diagram of the SSB wave in Figure 3 with envelope detection, and Figure 5 is a triangular wave and envelope-detected waveforms from a to b in Figure 4. It is an explanatory diagram for comparing and obtaining a PWM wave P. 1...SSB generation circuit, 2...Balanced modulator, 3...
...BPF, 4...Pre-stage amplifier, 5...Matching circuit,
6...SSB generation circuit, 7...Level shift circuit,
8... Triangular wave generator, 9... Comparator, 10
...Pulse amplifier, 11...LPF, 12...
BPF, 13...Limiting amplifier, 14...Pre-stage amplifier.

Claims (1)

[Claims] 1 A circuit that performs envelope detection of a single sideband wave and obtains a pulse width modulated wave obtained by using this and a triangular wave of a sampling frequency, and the above single sideband wave that is modulated by the demodulated wave of the pulse width modulated wave. A high-efficiency linear amplifier for SSB, characterized by comprising a switching power intensifier that is switched by the amplitude-limited amplified output of a sidepan wave.