JPS594210A - High efficiency linear amplifier for SSB - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention applies to 5SB which requires linear power amplification.
(single sideband) transmitter.

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 conventionally been used only for DSB (double sideband) broadcasting.

In DSB broadcasting, a carrier wave is always present, and this is transmitted as AM using audio.
However, it is well known that in the case of SSB broadcasts, the carrier wave is reduced or removed, and one side of the sideband is completely removed. In an SSB transmitter, the SSB wave is usually generated in a low-level stage, and the wave is sequentially amplified with good linearity. However, the problem is that the power efficiency is poor, and it is difficult to integrate the transmitter into an integrated circuit. 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, with conventional SSB transmitters, B
Class or AB amplification is used. FIG. 1 is a side view of the configuration of a conventional SSB transmitter, in which a normal linear amplifier is used. In Figure 1, AP is a low frequency input signal, 1 is an SSB generation circuit, 2 is a balanced modulator, fst f
s. is a carrier frequency input, 3 is a bandpass filter, 4 is a pre-stage amplifier, Q1Q2 is a field effect transistor (F E 'l'') forming a power amplifier section, 5 is a matching circuit,
Zo is the antenna load impedance. In order to perform linear amplification with this power amplifier circuit, it is necessary to apply a bias to the center point C on the gate side and to allow a certain amount of idle current to flow through F E 'I' Q and Q2 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, Q4. Q2 heat generation increases. Normally, when a small amount of idle current is passed through a class B amplifier, the power efficiency is in the 40s, but if it is made closer to a class A amplification in order to improve the distortion rate, the power efficiency drops to the 30% range. That is, the power loss will be close to 70%, and the QIQ2 cooling device will also be large.

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

FIG. 2 shows the configuration side of an SSB transmitter embodying the present invention. 6 in the figure is an SSB generation circuit, which converts the audio frequency AF to the carrier frequency f. Balanced modulation is performed by , and an SSB is obtained in which the fC component and one sideband, in this example, the lower sideband (or upper sideband) are removed. By the way, an SSB signal created from an audio signal has a waveform completely different from that of the original audio signal. Assume now that an SSB wave as shown in FIG. 3 is obtained. The original audio signal of this SSB wave cannot be obtained 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 detected by 5 envelopes,
The assigned frequency T5 wave (
The SSB wave is passed through the limiting amplifier 13, and the phase modulation remains, but the amplitude-radio wave is amplified and used as a carrier wave.) It is amplitude-modulated and transmitted as a normal SSB wave. Fig. 2 is explained below. do. Figure 4 is the third
This is a waveform diagram after envelope detection of the SSB wave shown in the figure, and corresponds to the f input in FIG. 2.

Returning to Figure 2, 7 is a level shift circuit, 8 is a triangular 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), and 13 is a limiting amplifier. , 14 is the front stage amplifier, Q
1 to Q4 are FETs that perform switching power amplification, Q5
is the switching FE'l"S'l"l 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 shown in FIG. 4 is at zero level. It is adjusted to zero by adjusting the voltage. The pulse P modulated in pulse width by the comparator 9 is shown in FIG.
The waveforms from a to b in the figure are enlarged and are usually 1. OOkHz
This shows how the pulse width is modulated by comparing it with the waveform of triangular wave B that takes a nearby sampling frequency.
The wave P is obtained in this way. This pulse P is amplified by a pulse amplifier 10 and applied to the gate of FETQ5. Q5 is therefore turned on in response to pulse signal P.
Perform the off action. 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. The sampling frequency component of the power turned on and off by Q5 is removed by LPFz, and the original envelope waveform becomes -Q, as modulated power.
1,7 Given to Q4.

On the other hand, the signal of assigned frequency f5 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 converted into a phase relationship (Ql and Q3 is 180, % and Q4 are 1
80, and Ql and Q2 have different phases by 180) to switch Q□ to Q4. Q1 to Q4 form a class D amplifier; for example, when Q□ and Mouse are on, Q3 and Mouse are off, and when Q3 and Q2 are on, Q
□ and then off, and alternately turn on and off according to the assigned frequency f. Q□~Q4 on the primary side of transformer T1
As the current flows, the polarity is reversed as the switch turns on and off.
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 load Z such as an antenna is removed.

is supplied with power having an envelope similar to the original SSB wave shown in FIG.

The above describes the power amplification of SiB waves, which requires particularly linearity.
Although we have explained the circuit specifically executed by class amplification, it has been confirmed that the power efficiency can be increased to nearly 80% according to actual measurements, and it is extremely effective in reducing the size of transmitters as a high-efficiency linear amplifier. .

[Brief explanation of drawings]

Fig. 1 is an example of the configuration of a conventional SSB transmitter, Fig. 2 is an example of the configuration of an SSB transmitter implementing the present invention, and Fig. 3 is an example of an SSB transmitter.
An example of the wave, Figure 4 is a waveform diagram of the SSB wave in Figure 3 with envelope detection, Figure 5 is a comparison of the triangular wave and the envelope-detected waveforms from a to b in Figure 4. FIG. 3 is an explanatory diagram for obtaining a PWM wave P. DESCRIPTION OF SYMBOLS 1...SSB generation circuit, 2...Balanced modulator, 30...BPF, 4...Pre-stage amplifier, 5...Matching circuit, 6...SSB generation circuit, 71- Fist level shift circuit, 8... triangular wave generator, 9 ■... comparator] 0... pulse amplifier, 11... L P Ii" 12... BPP 13... Limiting amplifier, 14...Pre-stage amplifier. Patent applicant Kokusai Denki Co., Ltd.

Claims (1)

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