JPH03104422A - Linear transmission equipment - Google Patents

Abstract

PURPOSE:To amplify a high speed modulation signal by using a saturation type power amplifier to constitute a linear transmission equipment applying power voltage control of an amplifier, and applying frequency equalization to an input signal of a DC voltage control circuit. CONSTITUTION:A frequency equalization circuit 10 connected between a correction circuit 6 and a DC voltage control circuit 7, receiving an envelope signal, applying amplitude and phase equalization of a signal taking an envelope signal as a variable and inputting its output signal to the DC voltage control circuit 7 is provided. The equalizing signal is inputted to the DC voltage control circuit 7 and the frequency characteristic of the DC voltage control circuit 7 has an improved high frequency characteristic, and its cut-off frequency reaches >=50kHz. Since the drain voltage VD of the power amplifier 4 is controlled with the output voltage of the improved DC voltage control circuit 7, high speed modulation signal is amplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is applied to a linear transmitter, and particularly relates to a linear transmitter including a power amplifier that amplifies with high efficiency a modulated wave signal whose envelope changes due to modulation. .

[Conventional technology]

Conventionally, the operating class of power amplifiers used in linear transmitters is class 8 or class AB.

This maintains linearity by setting the bias of the semiconductor amplification element so that the entire cycle of the input signal to the power amplifier is directly amplified into the output signal. but,
When the envelope of the input signal is small, the power efficiency of the power amplifier decreases. For this reason, portable radio devices that use batteries as a power source have the disadvantage that the batteries are consumed significantly and the operating time of the radio device is shortened.

In order to solve this problem, studies are being conducted on device structures that realize highly efficient linear transmitting devices.

FIG. 9 is a block diagram showing an example of such a linear transmitter, which uses a drain-controlled high-efficiency power amplifier disclosed in Japanese Patent Application No. 118786/1986.

In FIG. 9, 1 is a modulation input terminal, 2 is a modulator, 3 is a coupler, 4 is a saturation type power amplifier, 5 is an envelope detector,
6 is a correction circuit, 7 is a DC voltage control circuit, 8 is a power supply terminal, and 9 is a transmission output terminal. The power amplifier 4 includes an input matching circuit 41, a field effect transistor 42 as a semiconductor amplification element, a high frequency blocking coil 43, and an output matching circuit 44.

Next, the operation of this conventional example will be explained. Based on the modulation information (analog signal, digital signal) input from the modulation terminal l, a linear modulation wave signal is generated in the modulator 2 and amplified.At this time, the drain bias voltage Vn of the field effect transistor 42 is input. The envelope output level of the power amplifier 4 is made to follow the envelope of the human input signal by controlling it in approximately proportion to the envelope of the signal.With such control, the power amplifier 4 can be kept in a highly efficient saturated state. Since it can be operated as a linear amplifier, output distortion can be significantly reduced.

In addition, since the power amplifier 4 varies the drain voltage even when the input power is small and drains the amplifier almost in a saturated state, the power efficiency does not deteriorate significantly.

This drain control 1 word Vc is generated by a correction circuit 6 which detects the envelope signal of the modulated wave signal with an envelope detector 5 composed of a diode or the like, and performs a level shift between the detection signal and the control signal. It is obtained by applying correction, and this is converted to DC
- The voltage is applied to the drain bias terminal of the power amplifier 4 using a DC converter or, if necessary, a DC voltage control circuit 7 consisting of a series control transistor.

According to this conventional example, a linear transmitter using a highly efficient saturated power amplifier can be realized. For example, if a saturated amplifier with a power efficiency of 70% is used as the power amplifier 4 and a DC-DC converter with a power efficiency of 75% is used in the DC voltage control circuit 7, a linear transmitter with an overall efficiency of 50% or more can be realized.

Here, as the DC voltage control circuit 7, a DC-DC converter or a series control transistor is taken as an example.

In addition, a DC voltage control circuit using pulse width modulation, which is usually called a class S amplifier, can be applied. Step-down DC-DC converters and switching regulators have extremely similar operating principles.

[Problem to be solved by the invention]

However, in the conventional linear transmitter described above, the DC voltage control circuit 7 usually amplifies extremely low frequencies in order to obtain a constant output with respect to the input voltage, and the input/output cutoff frequency is extremely small < 10 KHz. That's about it. Therefore, in an amplifier for a modulated wave signal that fluctuates at a frequency higher than this cutoff frequency, the DC voltage control circuit 7 cannot follow changes in the modulated wave signal. As a result, distortion occurs in the output. For example, the frequency characteristics of a switching regulator depend on the control switch frequency, filter, etc. within the regulator. In order to modify this frequency characteristic, the frequency of the control switch may be increased, but the frequency is about 500 KHz at most, depending on the switching characteristics of the transistors and diodes that are the switches. For this reason, it is difficult to obtain sufficient frequency characteristics, and as a result, a sufficient linear transmitter cannot be realized for a modulated wave signal with a high modulation frequency.

An object of the present invention is to provide a linear transmitter that uses a conventional DC voltage control circuit and equivalently widens the input/output frequency characteristics with a simple structure by eliminating the above-mentioned drawbacks. .

[Means to solve the problem]

The present invention provides a modulation means for generating and outputting a modulated wave signal and its envelope signal by inputting a modulated information signal, a high frequency amplifier including a semiconductor amplifying element that receives the modulated wave signal as an input signal, and a high frequency amplifier for generating and outputting a modulated wave signal and its envelope signal. and a DC voltage control circuit that controls a DC power supply voltage applied to the power supply terminal of the high frequency amplifier according to a signal having a variable of . ,
The present invention is characterized in that it includes a frequency equalization circuit that inputs the envelope signal, equalizes the amplitude and phase of the signal using the envelope signal as a variable, and inputs the output signal to the DC voltage control circuit.

Further, the present invention may include a delay circuit that delays either the modulation signal or the envelope signal from the modulation means.

[Effect]

The frequency equalization circuit inputs the envelope signal from the modulation means, equalizes the amplitude and phase of the signal using the envelope signal as a variable, and inputs the output signal to the DC voltage control circuit.

Therefore, the frequency characteristics of the DC voltage control circuit are widened by the frequency equalization circuit, and as a result, it becomes possible to sufficiently satisfy the characteristics even for a modulated wave signal with a high modulation frequency.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG. 2 is a circuit diagram showing an example of a frequency equalization circuit thereof.

The first embodiment includes a modulator 2, a coupler 3, and an envelope detector 5 as modulation means for inputting a modulation information signal from a modulation input terminal 1 and outputting a modulated wave signal and its envelope signal. and a correction circuit 6, a field effect transistor 42 as a semiconductor amplification element which uses the modulated wave signal as a human input signal, an input matching circuit 41, a high frequency blocking coil 43, and an output matching circuit 44. In a linear transmitter comprising a power amplifier 4 and a DC voltage control circuit 7 that controls a DC power supply voltage supplied from a power supply terminal 8 applied to a power supply terminal of the power amplifier 4 according to a signal having the envelope signal as a variable. , which is a feature of the present invention, is connected between the correction circuit 6 and the DC voltage control circuit 7, inputs the envelope signal, and equalizes the amplitude and phase of the signal using the envelope signal as a variable. The frequency equalization circuit 1o is provided with a frequency equalization circuit 1o that performs the same operation and inputs the output signal to the DC voltage control circuit 7.

According to FIG. 2, the frequency equalization circuit 1o includes resistors R, ~R
6, capacitors cl and c2, and operational amplifiers l2 and l3. One ends of the resistors R and R6 are connected to the input terminal 11, the other end of the resistor R is commonly connected to the resistor R2, and one end of the capacitors c1 and C2, and the other end of the resistor R is grounded, and the other end of the resistor R is connected to the input terminal 11. C.I.
The other end of the capacitor c2 is connected to the output of the operational amplifier 12 along with the other end of the resistor R and one end of the resistor R, and the other end of the capacitor c2 is connected to the inverting input terminal of the operational amplifier 12 along with one end of the resistor R. The non-inverting input terminal of the amplifier 12 is grounded, and the other end of the resistor R4 is connected to one end of the resistor R and the resistor R6.
It is connected together with the other end to the inverting input terminal of the operational amplifier 13, the non-inverting input terminal of the operational amplifier 13 is grounded, and the output of the operational amplifier 13 is connected to the other end of the resistor R and the output terminal l4.

Next, the operation of this embodiment will be explained with reference to FIG. Here, FIG. 3 shows the frequency characteristics of the DC voltage control circuit 7 before and after frequency equalization, and also shows the frequency characteristics of the frequency equalization circuit 1.
This shows the frequency characteristics of 0.

In FIG. 3, curve A shows the frequency characteristics of the DC voltage control circuit 7 before frequency equalization, and its cutoff frequency is 10K.
It is below Hz. On the other hand, the frequency characteristic of the frequency equalization circuit 10 becomes as shown by curve B in FIG. 3 as a result of frequency equalization, and has a characteristic in which the amplitude becomes large in the high frequency range. This equalization signal is applied to the DC voltage control circuit g8. As a result, the frequency characteristics of the DC voltage control circuit 7 are improved as shown by curve C in FIG. 3, and the cutoff frequency is 5.
It becomes 0KHz or more. Due to the improved output voltage of the DC voltage control circuit 7, the drain voltage VD of the power amplifier 4
is controlled, it becomes possible to amplify a high-speed modulated wave signal.

Note that the frequency equalization circuit I having such frequency characteristics
O is an operational amplifier, as shown in FIG.
It can be easily constructed by including a resistor and a capacitor (author William, translated by Kato, "Electronic Filter", McGraw-Hill Publishing,
reference).

FIG. 4 is a block diagram showing a second embodiment of the present invention.

In the second embodiment, the present invention is applied to a linear transmitter having a modulation means different from that in the first embodiment shown in FIG.

The modulation means in the second embodiment includes a complex envelope generating circuit 21, digital-to-analog converters (D/A) 22 and 23 for in-phase or quadrature dividing envelope generation and orthogonal dividing envelope generation,
It includes a modulator section 2a including a quadrature modulator 24 and a carrier wave oscillator 25, and a drain control signal generation circuit 15.

The structure of the modulation section 2a is a known structure for generating a modulated signal based on changes in envelope and phase. That is,
The carrier wave angular frequency of the modulated wave is ω. , the envelope signal is R(t)
, the modulation phase is φ(1), then the modulated wave signal e (t)
is generally expressed as e(t)=R(t)・Re [exp(j
φt)゜exp(jωe1): ] =Re ['E(t)·exp(jωct))(1) It is expressed as follows. However, Re (・) represents the real part of [・]. Here, E (t) is called the complex envelope, and E (t) = I (t) − j Q ( t)
(2) I(t)=R(t) co sφ(1)
Q(t)−R(t) sinφ(t)
(3) becomes. I (t) and Q (t) are
They are called the in-phase and orthogonal parts of the complex envelope E (t).

In the complex envelope generation circuit 2■, 1 according to the modulation power
The values of (t) and Q (t) are calculated by digital processing. By converting the calculated values of I (t) and Q (t) into analog voltages by digital-to-analog converters 27 and 28, respectively, I (t) and Q
(t) waveform is obtained. These waveforms are input to the quadrature modulator 24. The quadrature modulator 24 multiplies I (t) and Q (t) by in-phase and quadrature carrier waves, respectively, to obtain a modulated wave signal e (t), which is output.

I (t) calculated by this complex envelope calculation circuit 21
The envelope signal R (t) can be determined using the values of and Q (t).

In the drain control signal generation circuit 15, R(t)=[1(t)2+Q(t)')"" (
4), the envelope signal R (t) can be obtained. The obtained envelope signal R (t) is output as is, or after being corrected to optimize drain control, it is converted into an analog voltage by a digital-to-analog converter and output from the drain control signal generation circuit 15. . The drain control signal output from this drain control signal generation circuit 15 is input to the frequency equalizer 10,
After being equalized to a sufficient control signal, it is applied to the DC voltage control circuit 7.

The DC voltage control circuit 7 operates so that the drain bias voltage Vn of the power amplifier 25 changes proportionally. By providing the frequency equalization circuit 10 in front of the DC voltage control circuit 7, it is possible to realize a linear transmitter that amplifies a highly modulated wave signal.

As the drain control signal generation circuit 15, a numerical arithmetic processor is used to generate manually generated I (t) and Q (t
) is used to obtain an envelope signal R (t) according to equation (4), and this is converted into an analog voltage by a digital-to-analog converter and output as it is or after correction. Moreover, it can be easily constructed by using a memory table in place of the numerical calculation processor.

FIG. 5 is a characteristic diagram showing an example of the spectrum of an envelope signal in the QPSK modulation method. In other words, the formula (4
) is the frequency distribution of the envelope signal R (t). However, the roll off=0.5 and the transmission speed is 32 Kb/s. In order to suppress the amplitude distortion of the power amplifier 4 to 50 dB or less, the frequency characteristics of the DC voltage control circuit 7 must include a spectrum component that is 50 dB lower than the DC component.

Therefore, it can be seen that a band of about 40 to 50 KHz is required in this case. As already explained in FIG. 3, the DC voltage control circuit 7 has a cutoff frequency of about 50 KH.
z or more, which fully satisfies this requirement.

The present invention is to easily realize speeding up of the control circuit in a linear transmitter that controls the power supply voltage of a power amplifier by equalizing the input and output frequencies of the DC voltage control circuit. Therefore, the power supply control signal does not necessarily have to match the envelope of the modulated wave signal, and even a signal close to the envelope can sufficiently exhibit this effect. In addition, the envelope of the power amplifier's manually modulated wave signal is constant;
It can also be applied to an AM transmitter that applies amplitude modulation using a power amplifier.

FIG. 6 is a block diagram showing a third embodiment of the present invention.

The third embodiment differs from the second embodiment shown in FIG. 4 in that delay circuits (τ>26 and 27, which are a feature of the present invention, are added before the digital-to-analog converters 22 and 23, respectively). be.

In FIG. 4, the DC voltage control circuit 7 includes a frequency equalization circuit l.
When O is inserted, the drain voltage V of the power amplifier 4 and the phase of the envelope from the output of the modulator section 2a are relatively delayed or advanced. The third embodiment is for a case where the drain voltage V of the power amplifier 4 lags behind the modulated wave input signal of the power amplifier 4 in its envelope phase. In this case, delay circuits (τ) 26 and 27, which can be constituted by a shift register or the like, are inserted to delay the modulated wave signal to match the phase of the drain voltage V of the power amplifier 25. Thereby, distortion due to control delay of the drain voltage V, can be reduced.

Also, if the lead and lag are opposite, that is, the 6th
In the third embodiment shown in the figure, even if the drain voltage Vn of the power amplifier 4 is delayed, it is possible to compensate for the delay difference. A fourth embodiment in this case is shown in FIG. Delay circuits 26 and 27 are inserted on the input side of drain control signal generation circuit 15. These delay circuits 26 and 27 delay the envelope signal, and can be realized by an analog circuit such as a delay line.The insertion point is the analog signal line, that is, the output of the drain control signal generation circuit 15, or the digital-to-analog converter 22. and 23 output side.

FIG. 8 shows the output spectrum of the power amplifier 4 according to the embodiment when using a 32 kb/s offset QPSK signal. When the DC voltage control circuit 7 is frequency-equalized, distortion improvement of about 5 to 10 dB can be seen.

In addition, in the above embodiment, as a semiconductor amplification element,
Although field effect transistors were used, the same applies to bipolar transistors.

Further, the present invention can be applied to a transmitting device in which frequency conversion is included between a modulator and a high frequency amplifier in which modulation is performed at an intermediate frequency.

〔Effect of the invention〕

As explained above, according to the present invention, a linear transmitter is constructed that controls the power supply voltage of the amplifier using, for example, a saturation type power amplifier, and by frequency equalizing the human input signal of the DC voltage control circuit. , it is possible to amplify higher-speed modulated signals, and the frequency equalization circuit has a simple structure, so a high-speed linear transmitter can be realized without increasing the number of parts, and its effects are large. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 2 is a circuit diagram showing an example of the frequency equalization circuit. Figure 3 shows its frequency characteristics. FIG. 4 is a block diagram showing a second embodiment of the present invention. FIG. 5 is a characteristic diagram showing the envelope spectrum. FIG. 6 is a block diagram showing a third embodiment of the present invention. FIG. 7 is a block diagram showing a fourth embodiment of the present invention. FIG. 8 is a characteristic diagram showing an example of an output spectrum according to an embodiment of the present invention. FIG. 9 is a block diagram showing a conventional example. DESCRIPTION OF SYMBOLS 1...Modulation input terminal, 2...Modulator, 2a...Modulator section, 3...Coupler, 4...Power amplifier, 5...
・Envelope detector, 6... Correction circuit, 7... DC voltage control circuit, 8... Power supply terminal, 9... Transmission output terminal,
10... Frequency equalization circuit, 1l... Input terminal, 12
, 13... operational amplifier, 14... output terminal, l5.
...Drain control signal generation circuit, 21...Complex envelope generation circuit, 22, 23...Digital to analog converter (D/A), 24...Orthogonal modulator, 25...Carrier wave oscillator, 26, 27...Delay circuit (τ>, 41...
- Input matching circuit, 42... field effect transistor, 4
3... Coil, 44... Output matching circuit, C. , C
．． ...Capacitor, R. ~R6...Resistance. 1st Yibako example (Ko and Rainbow answering mouth tower) 昂 2 Kairyo 1 Diagram A: JL 詑 11f: Rl Futagawa Yodera 5 (frequency customer C No. 4 Hi drug) 8: Pigeon crossing equalization times exposure C:,! Run! Oppression interpolation tower (Turtle in the ear of Zhou) Zhou''LL absorption (kHz) 0' 50k lj1'& board (floor) 100k Jiji's brother? Spectrum〉 38 Figure

Claims (1)

[Claims] 1. Modulation means (2, 2a, 3, 5, 15) that receives a modulation information signal and generates and outputs a modulated wave signal and its envelope signal.
, 25), a high frequency amplifier (4) including a semiconductor amplification element which receives the modulated wave signal as an input signal, and a DC power supply voltage applied to a power supply terminal of the high frequency amplifier according to a signal having the envelope signal as a variable. A linear transmitting device comprising a DC voltage control circuit (7) for controlling, connected between the modulation means and the DC voltage control circuit, inputting the envelope signal and using the envelope signal as a variable. A linear transmitter comprising a frequency equalization circuit (10) that equalizes the amplitude and phase of a signal and inputs the output signal to the DC voltage control circuit. 2. The linear transmitter according to claim 1, further comprising a delay circuit (26, 27) for delaying either the modulated signal or the envelope signal from the modulating means. .