JPH04578Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a circuit that uses MOS FETs to amplify broadband high-frequency power using a SEPP (Single Ended Push Pull) circuit.

(Prior Art) Conventionally, as this type of power amplifier circuit, those shown in FIGS. 3 and 4 are known. In Fig. 3, the input signal input to input terminal 1 is divided into opposite phases by secondary windings S1 and S2 of input transformer T1, and is excited between the gates and sources of MOS FETs TR1 and TR2. do. transistor tr
1. TR2 is connected in parallel to the load in AC mode and performs one SEPP operation as an AC output terminal, and the amplified output signal is combined by output coupling capacitors C3 and C4, and after impedance conversion by output transformer T2. It is output to output terminal 2.

Terminal 3 is a gate bias power supply terminal, and terminal 4 is a drain power supply terminal. C1 and C2 are gate bias DC cut capacitors, and C5 is a power supply bypass capacitor. Symbol CH1 is a gate bias voltage supplying coil, CH2,
CH3 is a choke coil for supplying MOS FET drain current. Further, symbols R1 and R2 are gate termination resistors.

(Problems to be solved by the invention) The problems to be solved in the conventional amplifier circuit as shown in FIG. 3 are as follows.

First, in this kind of SEPP circuit, the transistor
Since the source terminal of TR1 is the output terminal of the amplifier, the output voltage is superimposed on the secondary winding S1.
The output voltage is fed back to the winding S2 through the capacitance existing between the windings S1, S2, and P1 as shown in FIG. Good output characteristics cannot be obtained unless the excitation voltage of each MOS FET is uniformly applied between the gate and source terminals.
1. If there is a difference in the excitation voltage and phase of TR2, the push-pull balance will deteriorate, distortion will occur in the output waveform, high-order harmonics will increase in the broadband amplifier, and efficiency will also deteriorate.

Second, since no current flows through the insulated gate of the MOS FET, theoretically the excitation power is zero, but
Since there is an input capacitance Cg between the gate and source,
At high frequencies, an excitation current flows through this input capacitor. Because of this input capacitance, wideband amplifiers require more excitation power at higher frequencies, and the input terminal 1
The impedance characteristic becomes capacitive. For this reason, the gate termination resistor R is connected in parallel between the gate and the source.
1, R2 is inserted, but if you want to obtain uniformly good input impedance characteristics within the band of use, this resistance value should be sufficiently low compared to the reactance value of the input capacitance at the highest frequency of use. In order to make the power gain uniform within the band, it is necessary to use a gain compensation circuit or a negative feedback circuit, which has the disadvantage that the circuit becomes complicated and the power gain decreases.

Thirdly, in the circuit shown in Figure 3, the MOS FET TR
1. Chiyork coils CH2 and CH3 are required to supply the drain current of TR2.
Chiyoke coils CH2 and CH3 are wound around dust cores or ferrite cores to make them more compact.
Because it is excited by a high-frequency current with a superimposed direct current, magnetic saturation of the core is likely to occur, leading to a lack of inductance at low frequencies and deteriorating output characteristics. Furthermore, depending on the configuration of the input transformer T1, the phase rotation of the feedback voltage becomes severe, which causes parasitic vibration and self-oscillation to easily occur, resulting in a disadvantage that the operation of the amplifier becomes extremely unstable.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the drawbacks of the prior art, and to provide a wideband power amplifier circuit with high power gain, good output characteristics, and a relatively simple circuit configuration.

(Means for solving the problem) According to the present invention, by providing the input circuit with an input transformer with electrostatic shielding between the primary and secondary windings and a low-pass filter composed of L-C. ,
Equalizes the excitation voltage of the two MOS FETs, obtains a good push-pull balance, reduces output waveform distortion, increases the power gain so that excitation can be performed with the minimum excitation power, and utilizes the winding of the output transformer. do
By supplying the drain current of the MOS FET, the circuit configuration is simplified by eliminating the need for the choke coils CH2 and CH3, and it is characterized by stable and efficient operation and obtaining a good amplified output.

(Example) An example of the present invention shown in the drawings will be described in detail below. Components that are the same as or equivalent to those described in FIG. 3 are designated by the same reference numerals as used in FIG. 3. T3 is the input balun transformer, 5 is L1,
Low pass filter consisting of L2, C6, T4,
T5 is a gate input transformer, R3 and R4 are gate termination resistors, and T6 is an output transformer. Next, in the operation, first, to explain from the input side circuit of the amplifier, the input signal input from the input terminal 1 is unbalanced and balanced converted by the balun transformer T3, and then the input signal is converted to the coil L1.
and L2 to excite the primary windings of gate input transformers T4 and T5. The voltage appearing on the secondary side of the gate input transformer excites between the gates and sources of MOS FETs TR1 and TR2, and is terminated at the gate termination resistor. The primary winding/secondary winding ratio of the transformers T4 and T5 is 1:1, and the load on the secondary side of the transformer is the gate termination resistor R3 or R4 and the gate input capacitance Cg, so the input side in Fig. 1 is The circuit becomes a balanced π-type third-order low-pass filter as shown in the equivalent circuit of FIG.

L1, L2, C6, R3,
If each value of R4 is determined, the input signal is applied to the gates of TR1 and TR2 without attenuation within the band.

In this circuit, when the input impedance characteristics and output frequency characteristics are the same as those in the circuit shown in Fig. 3, the values of the gate termination resistors R3 and R4 are the same as the resistance R shown in Fig. 3.
Since the value of 1, R2 can be increased to more than twice the value, the power gain is more than twice that of the circuit shown in FIG.

Further, gate input transformers T4 and T5 are transformers wound on separate ferrite cores, and 1
Since an electrostatic shield is provided between the next winding and the secondary winding, the output voltage will not be fed back to the input of the lower MOS FET TR2, unlike the input transformer T1 shown in FIG. This eliminates any undesirable oscillation phenomena, and since all the input circuits are balanced circuits, the excitation balance is good and TR1 and
Since the excitation voltages of TR2 are equal and no phase shift occurs, push-pull amplification is performed efficiently and the harmonic content of the output becomes extremely small.

Next, regarding the output side circuit, the output transformer T6 has two primary windings P2 and P3, which are wound with the same number of turns around the same ferrite core. In addition, the drain of MOS FET TR1 is connected to winding P2.
DC current flows and winding P3 has MOS FET TR2
The drain DC current flows, but these two currents flow in opposite directions, and the magnetic flux caused by the DC cancels out, so magnetic saturation of the ferrite core does not occur, and deterioration of the output characteristics is prevented. In addition, the circuit coils CH2 and CH like the circuit in Figure 3 can be used.
3 and the coupling capacitor C4 are unnecessary, which is effective in simplifying the circuit configuration.

(Effect of the invention) As explained above, according to the invention, MOS
Despite the gate input capacitance of the FET, it is possible to obtain a high power gain, so the excitation power is less than half that of the conventional circuit, and the two MOS
Since the excitation balance of the FET is good, unnecessary drain current does not flow, improving efficiency, and reducing output waveform distortion, simplifying the harmonic removal circuit.
The drain current of the MOS FET is 1 of the output transformer.
Since the current flows through the secondary winding, there is no need for a drain current supply drain coil, which simplifies the circuit, and has the advantage of greatly improving the electrical characteristics of the amplifier.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure is an equivalent circuit diagram of the input circuit in Figure 1, and Figure 3 is an equivalent circuit diagram of the input circuit in Figure 1.
The figure is a diagram of a SEPP type broadband amplifier circuit using conventional MOS FETs, and FIG. 4 is a drawing showing the state of capacitive coupling between the windings of the input transformer in FIG. 3. 1...Amplification circuit input terminal, 2...Amplification circuit output terminal, 3...Gate bias power supply terminal, 4...Drain power supply terminal, T1...Input transformer, T2...
...Output transformer, P1...T1, primary winding, S
1, S2...T1, secondary winding, CH1...chiyoke coil for gate bias voltage supply, CH2,
CH3...Chiyoke coil for drain current supply,
R1, R2...Gate termination resistance, TR1, TR2
...MOS FET, C1, C2...gate bias DC cut capacitor, C3, C4...output coupling capacitor, C5...drain power supply bypass capacitor, T3...balance transformer, 5...low pass filter, L1, L2 ...Low pass filter coil, C6...Low pass filter capacitor, T4, T5...Gate input transformer, T6...
...Output transformer, P2, P3...Primary winding for T6, R3, R4...Gate termination resistance.

Claims (1)

[Scope of utility model registration request] It is a transformer input type, and a pair of MOS FETs are connected in series to separate CHI York coils for the DC power supply, and connected in parallel to each other, and are connected in parallel to the load for the AC output terminal. In a high-frequency broadband power amplifier circuit using a single-ended push-pull (SEPP) circuit, the input circuit includes the pair of
Connected to each gate terminal of MOS FET,
Two gate input transformers whose primary and secondary windings are electrostatically shielded, and the MOS FET connected to the primary side of each of the two gate input transformers.
Equipped with a balanced low-pass filter consisting of a coil and a capacitor, including the gate input capacitance of
and the output circuit is equipped with an output transformer in which a pair of primary windings wound in opposite phases to each other in place of the DC power supply coil are each connected in series with the MOS FET. Power amplifier circuit.