JPH04145713A - High frequency power amplifier - Google Patents

Abstract

PURPOSE:To increase the output synthesis efficiency at a high frequency even when an FET is subject to the effect of a high frequency component and a divided frequency component by setting the ground condition of plural FETs connected in cascade identically over a wide frequency. CONSTITUTION:A gate width of FETs Q1, Q2 and a gate width of a current source FETQ3 are set to 1mm respectively and a gate voltage VG3 of the FETQ3 is set to 0V. Thus, the FETs Q1, Q2 are operated by a current a half of the saturation current IDSS. Furthermore, the capacitance of high frequency short-circuit capacitors C1, C2 is set identical to set the ground condition of the FETs Q1, Q2 over a wide frequency range. Thus, even when the FETs Q1, Q2 are in operation with a high output and affected by higher harmonic and divided frequency components due to the nonlinear component, they are operated in the same operating condition and the combination efficiency of high frequency power is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high frequency power amplifier, and more particularly to a high output high frequency power amplifier using a field effect transistor (CFET).

[Conventional technology]

FIG. 3 shows an example of a conventional high-frequency, high-output amplifier, particularly an amplifier designed to be connected in cascade, operated at a high power supply voltage, and to reduce operating current.

In FIG. 3, a conventional high-frequency power amplifier, that is, an amplifier circuit 1, has input circuits 11 and 12 including an input coupling capacitor and an input matching circuit, and output circuits 13 and 14 including an output matching circuit and an output coupling capacitor. , FETQl,Q
2, a high frequency short circuit capacitor C1l, and high frequency choke coils L1 and L2.

By connecting FETQl and Q2 in series to the power supplies vI and l) and operating them with the same current IDD, a single FET
This is an amplifier that can be operated at a power supply voltage DD higher than the withstand voltage of DD.

Generally, the breakdown voltage of FET is about 20V at most.
Its DC operating voltage is kept to about 10,000 volts, which is the withstand voltage.

Therefore, the operating voltage of the FET is usually set to 10V or less.

However, a transmitter using this type of microwave power amplifier usually has a power supply with a high power supply voltage of 15V to 26V, and this voltage is stepped down and supplied to the FET.

For this reason, power is consumed during step-down, reducing the power efficiency of the entire device.

Therefore, if the amplifier can be operated with a high power supply voltage, it is often possible to improve the power efficiency of the entire transmitter.

A circuit devised for this purpose is a conventional amplifier circuit shown in FIG. An input circuit 11.12 and an output circuit 13.14 are provided for each FETQI, Q2, and a power supply v,
By connecting the choke coils L1 and L2 to D and the capacitor C1 for high frequency shorting, and composing the input circuits 11, 12 and output circuits 13 and 14, it is possible to obtain twice the output. Moreover, there is an advantage that the operating current IDD can be operated with a current equivalent to one FET.

[Problem to be solved by the invention]

In this conventional high-frequency power amplifier, a capacitor for high-frequency shorting is used to ground the FET on the high potential side in terms of direct current, but the value of this capacitor cannot be made infinite, that is, the impedance cannot be made zero. Therefore, there was a drawback that it was impossible to obtain a perfect optical grounding.

For this reason, the FET on the high potential side and the FE on the low potential side in terms of DC
The grounding conditions of T are different, and especially during high output operation, the operation of both FETs is affected by the harmonic number component and its ten frequency components due to nonlinear characteristics, resulting in imbalance and a decrease in the RF' power synthesis efficiency. There was a problem.

That is, the practically selectable value of the capacitor for high frequency grounding is on the order of several thousand PF at a frequency of IGHz, and the impedance at this time is about 1Ω. On the other hand, F
Since the source resistance of the ET is about 1 Ω, there is a problem in that if the influence of the capacitor on the nonlinear characteristics is ignored, a combined loss of about 1 dB occurs.

[Means to solve the problem]

The high frequency power amplifier of the present invention is a high frequency power amplifier in which a plurality of field effect transistors for power amplification are connected in cascade to a power source, and the field effect transistor for power amplification is connected between the source of the field effect transistor for power amplification, which is at a high potential in terms of DC potential, and the ground. a second capacitor having the same capacitance as the first capacitor connected between the source of the power amplifying field effect transistor which is at a low DC potential and the ground; and the second capacitor connected to the ground. and a DC bias circuit connected in parallel.

〔Example〕

Next, the present invention will be explained with reference to the drawings. 1st
The figure is a circuit diagram showing one embodiment of the present invention.

In FIG. 1, the high frequency power amplifier of this embodiment has an amplifier circuit 1 similar to the conventional one, and an FE on the low potential side in terms of DC.
It has a configuration in which a capacitor C2 for grounding the source of TQ2 at high frequency and a current source FETQ3 for a bias circuit are added.

Here, the gate width of FETQI and Q2 is
, the gate width of current source FETQ3 is 1mm, and Q3
The gate voltage V. By setting 3 to Ov, FETQ
I and Q2 can be operated with a current that is half the saturation current IDSS.

Furthermore, by setting the capacitors C1 and C2 for high frequency shorting to have the same capacity, the grounding conditions of the FETs QI and Q2 can be set to be the same over a wide frequency range.

Therefore, even if these FETs QI and Q2 operate at high output and are affected by harmonics and frequency components of frequency division due to nonlinear components, they can be operated under the same operating conditions, resulting in high frequency power synthesis efficiency. can be raised.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

In FIG. 2, the difference between this embodiment and the first embodiment shown in FIG. , by connecting a series circuit with the high frequency choke coil L3.

In this embodiment as well, by setting the resistor R1 to about 10Ω, the voltage drop to 1V, and setting VGI to zero volts, the operating current of FETQI and C2 can be reduced to about 10Ω. , S can be set.

Further, since the source impedance can be set equally for these FETs, power synthesis efficiency can be increased.

〔Effect of the invention〕

As explained above, the present invention has a plurality of cascade-connected FEs.
By setting the T grounding conditions equally over a wide range of frequencies, the same operating conditions can be maintained even when the FET is affected by harmonics and their subfrequency components due to the nonlinear characteristics of high-output operation. , the high frequency output synthesis efficiency can be increased, and therefore the efficiency of the entire high frequency power amplifier can be increased.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the invention, and FIG. 3 is a circuit diagram showing an example of a conventional high frequency power amplifier. 1...Amplification circuit, 11.12...Input circuit, 13゜14...Output circuit, C1,, C2
... Capacitor, L1 to L3 ... High frequency choke coil, Q1 to Q3 ... Field effect transistor (FET). Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] 1. In a high frequency power amplifier in which a plurality of field effect transistors for power amplification are connected in cascade to a power source, a connection between the source of the field effect transistor for power amplification, which is at a high potential in terms of DC potential, and ground. a second capacitor having the same capacitance as the first capacitor connected between the source of the power amplifying field effect transistor which is at a low DC potential and the ground; and the second capacitor connected to the ground. and a DC bias circuit connected in parallel. 2. The high frequency power amplifier according to claim 1, wherein the DC bias circuit is a current source formed by a source-grounded field effect transistor having a gate having the same gate width as the power amplifying field effect transistor.