JPS62220009A - Broad band power amplifier - Google Patents

Abstract

PURPOSE:To eliminate harmonics of the lower limit frequency by extracting a signal at the lower limit frequency of an amplifier and using the signal to switch a pin diode element. CONSTITUTION:When a signal at the lower limit frequency band of the amplifier is inputted, a series resonance circuit comprising an inductor element 32 and a capacitor 33 is resonated. Then a part of the signal appears at the anode side of a detection diode 35, the signal is detected by the detection diode 35 and a DC signal is obtained, which is inputted to an arithmetic unit 39 via a resistor 38. When an output voltage of an operational amplifier 39 reaches a prescribed value or over, a switching transistor (TR) 44 is turned on and a switching TR 49 is turned off, a pin diode 27 is turned on and a pin diode 55 is turned off. a parallel resonance circuit comprising a capacitor 25 and an inductor element 26 is the pass band at the lower limit frequency and has an infinite impedance at a frequency twice the lower limit frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an amplifier used in a radio device, etc., and particularly to a wideband power amplifier with a wide band, high output, and few harmonics.

Conventional technology Conventionally, this type of amplifier has a wide required frequency band of more than one octave and is required to have a high output, so it has many harmonics, and it is extremely difficult to remove the harmonics. Ta. For example, if the input frequency of the amplifier is the lower limit of the required frequency band (denoted as fL), the harmonic 2fL, which is twice that frequency, is the lower limit of the required frequency band. Therefore, it is difficult to remove such harmonics 2fL with matching circuits, low-pass filters, etc. Therefore, it is necessary to use transistors with high output and high dynamic range that do not generate such harmonics. It was necessary to make a selection.

Problems to be Solved by the Invention As mentioned above, in conventional wideband amplifiers, the harmonics are determined by the selected transistor elements, and in developing an amplifier with extremely low harmonics (particularly second harmonics), the first step is to select transistor elements. We must start by selecting the elements. However, this is extremely difficult. The transistor is
The usage conditions are also limited, and transistor elements that suppress harmonics as much as possible are generally expensive, so amplifiers that use complex stages of such transistors have the problem of becoming extremely expensive. there were.

Therefore, the present invention eliminates the conventional drawbacks and eliminates harmonics, especially 2
It is an object of the present invention to provide a wideband power amplifier that can remove double harmonics.

According to the present invention, a means for solving the problem is a broadband power amplifier circuit, a first pin diode connected to the output of the power amplifier circuit, and a first pin diode connected in parallel to the first pin diode. an LC parallel resonant circuit, an LC series resonant circuit having one end connected to the input side of the first pin diode, and a termination means connected to the other end of the LC series resonant circuit via a second pin diode. and a control circuit connected to the input stage of the power amplifier circuit to detect the frequency component of the input signal and selectively turn on one of the two pin diodes and turn the other one off. (rir+) is provided.

In the broadband power amplifier according to the present invention, such as more than one month,
When the LC parallel resonant circuit and the LC series resonant circuit are in a resonant state, the LC parallel resonant circuit functions as an infinite impedance, and the LC series resonant circuit functions as an impedance atmosphere.

Therefore, if the resonant frequencies of the LC parallel resonant circuit and the LC series resonant circuit are set to the harmonic frequency of the input signal of a predetermined frequency, the control circuit detects that the predetermined frequency component substantially occupies the input signal. At this time, harmonics of the input signal of a predetermined frequency can be removed by turning off the first pin diode and turning on the second pin diode.

That is, in this state, harmonic components of the input signal are released to the termination means via the LC series resonant circuit that functions as zero impedance for the harmonics and the pin diode in the on state.

On the other hand, the harmonic components of the input signal cannot pass through the first pin diode that is in the off state, and are also blocked by the LC parallel resonant circuit, which functions as an infinite impedance for the harmonics. Ru.

Therefore, harmonic components are not output.

On the other hand, with respect to the fundamental wave component of the input signal, the LC series resonant circuit has substantial impedance, and the LC parallel resonant circuit has low impedance. Therefore, the fundamental wave component of the input signal is outputted via the LC parallel resonant circuit without being released to the termination means via the LC series resonant circuit.

However, in cases other than the above, the control circuit turns on the first pin diode and turns off the second pin diode. Therefore, the output signal is output via the first pin diode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings. The attached FIG. 1 is a circuit diagram showing an example of a wideband power amplifier embodying the present invention.

The input of a preamplifier 3 is connected to the input side 1 via a coupling capacitor 2, and the preamplifier 3 is connected to another one.
Two preamplifiers 4 are connected. The preamplifier 4 is connected to the gate of a field effect transistor (hereinafter referred to as FET) 11 via a coupling capacitor 5, and the source of the FET 1l is grounded. The gate of the FET is connected via a current limiting resistor 6 to an intermediate connection point between voltage dividing resistors 8 and 9. The other end of the resistor 8 is grounded, and a high frequency blocking capacitor 7 is connected in parallel to the resistor 8.

On the other hand, the other end of the resistor 9 is connected to a power supply terminal 10.

The drain of FET II is connected to the power supply terminal 20 via the smoothing coil 13, and a high frequency blocking capacitor is connected to the end of the smoothing coil 13 on the power supply terminal 20 side. Further, the drain of FET 11 is connected to the gate of another FE'T 19 via a coupling capacitor 14. Its gate is also connected to an intermediate connection point between voltage dividing resistors 16 and 17 via a current limiting resistor 15. The other end of the resistor 17 is grounded, and a high frequency blocking capacitor 18 is connected in parallel. On the other hand, the other end of the resistor 16 is connected to the power supply terminal 1
Connected to 0. Further, the source of FET II is grounded, and the drain is connected to the power supply terminal 20 via the smoothing coil 23, and a high frequency blocking capacitor is connected to the end of the smoothing coil 13 on the power supply terminal 20 side. has been done.

Furthermore, the drain of the FET 11 is connected to a coupling capacitor 23,
It is connected to an output terminal 30 via a pin diode 27 and a coupling capacitor 29. That pin diode 27
The cathode of is grounded via a resistor 28, and both pin diodes 27 (11) are connected to a coupling capacitor 24.
A parallel resonant circuit consisting of a capacitor 25 and an inductor 2G is connected in parallel through the capacitor 25 and the inductor 2G.

On the other hand, the anode of the pin diode 27 is connected to the inductor 5.
3 and a capacitor 53 to the anode of another pin diode 55. The cathode of the pin diode 55 is grounded via a resistor 58 and connected to a non-reflective terminator 57.

Further, a series resonant circuit consisting of an inductor 32 and a capacitor 33 is connected to the coupling capacitor 2 via a resistor 31. And, at the output end of the capacitor 33,
An RF signal dividing resistor 34 is connected, and one end of a detection diode 35 is also connected.

The other end of the detection diode 35 is connected to a high frequency blocking capacitor 36 and a load resistor/variable resistor 37. A variable terminal of the variable resistor 37 is connected to a non-inverting input of an operational amplifier 39 via a human resistor 38. The inverting input of the operational amplifier 39 is connected to ground via a resistor 40 and to the output via a resistor 41, which determine the DC amplitude of the amplifier.

The output of the operational amplifier 39 is connected to the base of a first switching transistor 44 via a constant voltage diode 42 and a current limiting resistor 43. The emitter of the switching transistor is grounded, and the collector is resistor 4.
5 to the positive power supply terminal 46. The first
The collector of the switching transistor 44 further includes:
The second
The base of the switching transistor 49 is connected to the base of the switching transistor 49. This capacitor 47 is a speed-up capacitor that corrects the time constant caused by the resistor 48 and the BE capacitance of the switching transistor 49. The second
The emitter of the switching transistor 49 is also grounded, and the collector is connected to the positive power supply terminal 46 via the resistor 50.

Therefore, the collector levels of switching transistors 44 and 49 are opposite to each other. The collector of the switching transistor 44 is connected to the anode of the pin diode 27 via the current limiting resistor 51.
Furthermore, it is also connected to a high frequency blocking capacitor 52. Moreover, the collector of the switching transistor 49 is
It is connected to the anode of pin diode 55.

In the wideband amplifier as described above, RF
When a doubled signal is input, the RF multiplied signal is amplified by the preamplifier 3.4, further amplified by the FET II, 19, and high power is output from the output terminal 30.

Now, the band of a wideband amplifier is designed to be one octave, the lower limit frequency is fL, the upper limit frequency is fll, and the center frequency is ``.

Assume that the RF multiplied signal having the frequency fL is input to the input terminal 1. The second harmonic 2ft of the frequency fL of the RF multiplied signal is the upper limit of the band of the amplifier (f, ,
1), it has conventionally been difficult to remove its second harmonic "2fL".

In the illustrated embodiment, such harmonics can be suppressed to a desired value, as described below. The series resonant circuit of the inductor element 32 and the capacitor 33 is set in advance so that it resonates at the frequency "," when the RF multiplied signal having the lower limit frequency rL of the band of the amplifier is input. A part of the RF multiplied signal appears on the anode side of the diode 35, and is detected by the detection diode 35 and converted into a DC signal.This converted DC signal is divided into desired values by the variable resistor 37. ,
Power is supplied to an operational amplifier 39 via a resistor 38.

Now, connect the variable resistor 37 and the resistor 40.41 so that the output voltage of the operational amplifier 39 is higher than a predetermined voltage (■,) (composition of the Zener voltage of the constant voltage group and the B-E voltage of the switching transistor 44). If the switching transistor 44 is turned on and the switching transistor 49 is turned off, the pin diode 27 is turned on and the pin diode 55 is turned off.

If the parallel resonant circuit (capacitor 25, inductor element 26) and series resonant circuit (inductor element 53, capacitor 54) are set in advance to resonate at a frequency of 2fL ("f++"), the parallel resonant circuit will be able to operate at the human frequency. At fL, it is a passband, and at fL, it has a maximum impedance of IW and becomes a circuit breaker.On the other hand, the series resonant circuit has an impedance of 1lji (minimum impedance) at the input frequency fL, It becomes a passing area.

In this way, when the RF multiplied signal having the frequency fL appears at the input terminal 1, the fundamental frequency fL is outputted to the output terminal 30 with the gain of the amplifier, and the harmonic 2fL is reflected by the parallel resonant circuit. It is absorbed by the non-reflection terminator 57.

Next, when the input frequency is gradually increased, the impedance of the series resonant circuit (inductor element 32, capacitor 33) increases, the DC signal from the detection diode 35 decreases, the output voltage of the operational amplifier 39 decreases, and the voltage becomes constant. The voltage diode 42 is cut off, the switching transistor 44 is turned off, and the switching transistor '49 is turned on. Therefore, the pin diode element 27 is turned on.
Pin diode element.

55 is turned off, and the frequency fLL is higher than the input frequency fL.
The RF multiplied signal having a frequency from to fu is outputted to the output terminal 30 via the pin diode element 27 without loss.

Of course, by adjusting the Q of the series resonant circuit (inductor element 32, capacitor 33) and the variable resistor 37,
It goes without saying that the frequency fLL at the threshold point can be set freely.

As described in the detailed description of the invention, the wideband power amplifier according to the present invention comprises:
It is configured so that a part of the RF multiplied signal can be extracted only at the lower limit of the frequency band of the amplifier, and the pin diode element is switched depending on the extracted signal. Therefore, the harmonics of the lower limit frequency (especially the second harmonic) can be removed, and no external signals are required, making it easy to design peripheral devices, and without using expensive transistors. It is possible to design a powerful amplifier.

[Brief explanation of drawings]

The attached FIG. 1 is a circuit diagram of a broadband amplifier embodying the present invention. [Main reference numbers] 1...Input side 3.4...Preamplifier

Claims (1)

[Claims] a broadband power amplifier circuit, a first pin diode connected to the output of the power amplifier circuit, an LC parallel resonant circuit connected in parallel to the first pin diode, and an input of the first pin diode. an LC series resonant circuit having one end connected to the side; a termination means connected to the other end of the LC series resonant circuit via a second pin diode; a control circuit that detects a frequency component of the pin diode and selectively turns one of the two pin diodes on and the other one off.