JPS5846567Y2 - Bias circuit for high frequency transistor class C amplifier - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a bias circuit for a high frequency transistor class C amplifier.

A transistor class C amplifier requires a bias circuit that connects the input terminal of the transistor (the base terminal in the normal case where the transistor is used with its emitter grounded) to ground in terms of direct current and is open in terms of high frequencies.

When a high frequency circuit on UHFHF is configured with a distributed constant line, this bias circuit can be realized with the configuration shown in FIG.

In FIG. 1, 1 is a transistor with a common emitter, and 2 is a distributed constant line with a length of 1/4 wavelength.

The impedance viewed from the base terminal 9 to the distributed constant line 2 is grounded in terms of direct current and open in terms of high frequency.

In the basic configuration shown in Fig. 1, unnecessary oscillations often occur at low frequencies outside the band, so in reality, the basic configuration shown in Fig. 2a is used.

The configuration shown in b is used.

In FIGS. 2a and 2), 11.21 is a transistor with a common emitter, 12.22 is a distributed constant line with a length of 1/4 wavelength, and 13.23 is a resistor.

In the basic configuration shown in Figure 1, from the base terminal 9 to the distributed constant line 2
The impedance seen in Figure 2 becomes pure reactance at the frequency where unwanted oscillation occurs (usually 1/10 to 1/2 of the band center frequency) and has no loss component, but if the configuration shown in Figure 2 is used,
The resistors 13 and 23 include loss components at low frequencies outside the band, making it possible to prevent unnecessary oscillations.

However, the configuration shown in FIG. 2 has the following drawbacks.

First, in the configuration shown in FIG. 2a, the impedance when looking at the bias circuit from the base terminal 19 is open at high frequencies;
It is not grounded in terms of direct current.

Therefore, the bias point changes depending on the DC base current of the transistor 11.

Since the DC base current of the transistor depends on the magnitude of the high frequency input power, the DC bias point ultimately changes depending on the magnitude of the high frequency input power.

The direction of change is such that as the high-frequency input power increases, the bias point increases to the negative side, that is, the gain of the transistor decreases.

In order to reduce the gain as much as possible, the resistance value of the resistor 13 is usually set to a small value of 10 g or less, but of course it is impossible to eliminate it completely.

On the other hand, in the configuration shown in Figure 2, the impedance seen from the base terminal 29 to the bias circuit is grounded in terms of DC, but
It is not open at high frequencies.

Since a loss component due to the resistor 23 is also included in high frequency, high frequency input power is lost.

In order to reduce this loss as much as possible, the resistance value of the resistor 23 is usually set to a large value of 100Ω or more, but it is impossible to completely eliminate the loss.

In other words, the impedance required for the bias circuit is grounded for direct current so as not to reduce the gain, is open at high frequencies to eliminate input power loss, and contains a resistive component at low frequencies to prevent unnecessary oscillations. This is a necessary condition.

However, it has not been possible to create a bias circuit that simultaneously satisfies the above three conditions using the conventional configuration described above.

The purpose of this invention is to create a bias circuit that satisfies the above three conditions at the same time, in other words, a high-frequency transistor C that can prevent gain reduction, input power loss, and prevent unnecessary oscillations.
An object of the present invention is to provide a bias circuit for a class amplifier.

According to this invention, a 1/2 wavelength distributed constant line whose one end is connected to the input terminal of the transistor and a parallel connection circuit with a resistor has a 1/4 wavelength distributed constant line whose tip is grounded at the other end. A bias circuit for a characteristic high-frequency transistor class C amplifier is obtained.

FIG. 3 is a diagram showing an embodiment of this invention, in which 31 is a transistor, 32 is a distributed constant line with a length of 1/2 wavelength, and 33 is a diagram showing an embodiment of this invention.
is a distributed constant line with a length of 1/4 wavelength, and 34 is a resistor.

In FIG. 3, the impedance viewed from the connection point 38 of the two distributed constant lines to the side of the distributed constant line 33 is grounded in terms of DC and open in terms of high frequencies, but becomes a finite pure reactance at low frequencies.

Therefore, the impedance viewed from the base terminal 39 of the transistor to the bias circuit is grounded in terms of direct current and open in terms of high frequencies, and also includes a loss component due to the resistor 34 at low frequencies, so all three desired conditions can be satisfied.

Therefore, unlike conventional bias circuits, there is no limit to the value of the resistor 34, and any resistance value that can prevent unnecessary oscillations can be selected.

As explained in detail using the drawings above, the bias circuit of the high-frequency transistor class C amplifier according to this invention is practically effective because it can prevent unnecessary low-frequency oscillations without reducing gain or loss of input power. It is.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the basic configuration of a bias circuit of a high frequency transistor class C amplifier, and 2 is a 1/4 wavelength distributed constant line. FIGS. 2a and 2l) are circuit diagrams showing the configuration of a bias circuit of a conventional high-frequency transistor class C amplifier, and 12 and 22 are 1/4 wavelength distributed constant lines. Figure 3 is a circuit diagram showing the configuration of the bias circuit of the high frequency l.Randisuf class 0 amplifier according to this invention.
/2 wavelength distributed constant line, and 33 is a 1/4 wavelength distributed constant line.

Claims (1)

[Scope of utility model registration request] A high-frequency transistor characterized in that a parallel connection circuit of a 1/2 wavelength distributed constant line and a resistor, one end of which is connected to the input terminal of the transistor, and a 1/4 wavelength distributed constant line whose tip is grounded is connected to the other end of the circuit. Bias circuit for class C amplifier.