JP4835958B2 - High-frequency amplifier, pulse radar including the same, and method for blocking noise output - Google Patents

Description

  The present invention relates to a high-frequency amplifier circuit technique, and more particularly, to a high-speed cutoff technique for an amplification operation in a high-frequency amplifier used in a transmission unit such as a pulse radar and a microwave application apparatus.

  Currently, there are pulse radar and FM-CW radar as radars. Hereinafter, the basic principle will be described.

  In pulse radar, the distance is obtained by measuring the round trip time of a high frequency (radio wave) pulse, and the velocity is obtained by measuring the Doppler frequency from the difference between the transmitted wave and the received wave. Accordingly, the distance is obtained by signal processing in a time space, and the speed is obtained by processing in a frequency space. As a feature of the pulse radar, the transmission time and the reception time can be divided, so that the entire antenna can be made small by sharing the transmission and reception. On the other hand, for the same reason, reception is not possible when transmission pulses are being transmitted. Therefore, it is necessary to devise an extremely short pulse width for short distance measurement.

  A basic configuration of the FM-CW radar is shown in FIG. In the FM-CW radar, a high frequency with a constant output is continuously transmitted from the transmitter toward the target. The frequency of the high frequency is modulated to change with time (change rate is constant) as shown in FIG. 6, and the distance and speed are measured by measuring the frequency difference between the transmitted wave and the received wave. Therefore, unlike pulse radar, both distance and speed appear as frequency information. In FM-CW radar, since the transmission wave is always emitted, the antenna cannot be shared between transmission and reception. However, in principle, the distance is determined from the frequency difference between the transmission wave and the reception wave. It can be measured up to that point. However, since both the distance information and the speed information are in the frequency space, there is a disadvantage that a dead zone occurs.

  By the way, as a result of the inventor's examination of the pulse radar technology as described above, the following has been clarified.

  For example, when measuring up to a short distance with a pulse radar, in addition to measures to shorten the pulse width, the noise output from the transmitter is shut off immediately after the transmission pulse is transmitted so that the noise does not enter the receiver. It is necessary to improve the isolation of the receiver. In order to cut off the transmitter noise, measures such as cutting off the transmitter power supply and separating the transmitting and receiving antennas are taken. Thus, in the pulse radar, it is possible to measure to a closer distance by cutting off the noise output from the transmitter immediately after emitting the transmission pulse.

  The problem to be solved by the present invention is to quickly cut off the transmission output. For shutting off the transmitter output, there is a method of shutting off a high frequency amplifier power source or by installing a switch such as a PIN diode on an RF (radio frequency) line. However, the power supply voltage (drain voltage) of the field effect transistor used in the high frequency amplifier is about 10 V, and it is difficult to obtain a high speed switch at the speed of the FET switch used for blocking. The method of loading a PIN diode on the RF line can obtain a sufficiently high cutoff speed, but there is a problem with the withstand power, which limits the transmitter output.

  Accordingly, an object of the present invention is to provide a technique that can quickly cut off a transmission output and reduce a noise output in a high-frequency amplifier used in a transmission unit such as a pulse radar.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  In the present invention, the field effect transistor (FET) used in the high-frequency amplifier is cut off by the operating point transition rather than the high voltage drain voltage. Focusing on the fact that field-effect transistors used in high-frequency high-frequency amplifiers are generally used in class A operation, changing the gate voltage at a low voltage at high speed, the field-effect transistor operates in class C By setting the state, the amplification function of the field effect transistor can be significantly reduced. Even if the power supply of the field effect transistor does not drop due to the transition of the operation state from the class A to the class C, the noise output from the high frequency amplifier can be cut off by significantly reducing the amplification function of the field effect transistor.

  According to the present invention, in a field effect transistor of a high-frequency amplifier, the gate voltage of the high-frequency amplifier is controlled by controlling the gate voltage with a small voltage and a small amount of current without blocking the drain voltage / current with a high voltage and a large current. Noise output can be reduced.

  Therefore, according to the present invention, it is possible to relatively easily reduce the short-range measurement limit of the pulse radar. Conventionally, even in the case where the transmitting and receiving antennas are separated for isolation, A small antenna can be made lighter by using a transmission / reception antenna.

It is a circuit diagram which shows the structural example of the pulse radar by one embodiment of this invention. FIG. 2 is a circuit diagram illustrating a configuration example of a high-frequency amplifier illustrated in FIG. 1. It is a figure which shows the signal waveform in each location of the high frequency amplifier shown in FIG. FIG. 3 is a diagram showing a waveform of a gate voltage of a field effect transistor at the final stage of the high-frequency amplifier shown in FIG. 2. It is a figure which shows the example of a basic composition of FM-CW radar in the technique examined as a premise of this invention. In the technique examined as a premise of this invention, it is a figure which shows the frequency modulation example of FM-CW radar.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

  FIG. 1 is a circuit diagram showing a configuration example of a pulse radar according to an embodiment of the present invention.

  First, an example of the configuration of the pulse radar according to the present embodiment will be described with reference to FIG. The pulse radar according to the present embodiment includes, for example, a transmission unit including a high frequency generation unit 102 and a high frequency amplifier 103, a reception unit including a low noise amplifier 106 and a demodulation circuit 107, and signal processing for processing transmission and reception signals. The unit 101, a circulator 104 that switches between transmission and reception, a transmission / reception shared antenna 105 for transmission and reception, and the like.

  This pulse radar generates a high frequency signal in the high frequency generator 102. This high frequency signal is modulated with a pulse signal from the signal processing unit 101, and a continuous high frequency signal is formed into a pulsed high frequency signal. The shaped pulsed high-frequency signal is amplified by the high-frequency amplifier 103 and transmitted as a radio wave from the shared antenna 105 via the circulator 104. The signal transmitted by radio from the transmission / reception shared antenna 105 hits an object, and the reflected wave is received by the shared transmission / reception antenna 105. The radio wave received by the shared antenna 105 is amplified by the low noise amplifier 106 via the circulator 104, demodulated into a pulse signal by the demodulation circuit 107, and signal processed by the signal processing unit 101. The signal processing unit 101 measures the round trip time of a high-frequency signal (radio wave) pulse to determine the distance of the object, and measures the Doppler frequency from the difference between the transmitted wave and the received wave to determine the speed of the object. That is, the distance is obtained by signal processing in a time space, and the speed is obtained by processing in a frequency space. As a feature of this pulse radar, since the time of transmission and the time of reception can be divided, the entire antenna can be made small by sharing the transmission and reception.

  FIG. 2 is a circuit diagram showing a configuration example of the high-frequency amplifier 103 shown in FIG.

  As shown in FIG. 2, the high-frequency amplifier 103 includes, for example, a power supply pulse generation unit including a NAND gate N1, drivers D1, D2,..., Dh, a transistor T1, an inductor L2, and the like, a NAND gate N2, a Zener diode Z1, A cut-off pulse generator comprising a resistor R1, a capacitor C2, and a NAND gate N3, a gate bias generator comprising a resistor R2, a variable resistor R3, an inductor L1, etc., a preamplifier (Amp) A1, and capacitors C1, C3 C4, transistor T2, and the like. The number of drivers D1, D2,..., Dh may be one (only D1).

  The transistor T2 amplifies the high frequency signal (RFIN) and outputs RFOUT. The power pulse generator generates a power pulse and applies the power pulse to the drain of the transistor T2. The gate bias generation unit generates a gate bias voltage and applies the gate bias voltage to the gate of the transistor T2. The cutoff pulse generation unit generates a cutoff pulse signal when the power supply pulse is cut off, and applies the cutoff pulse signal to the gate of the transistor T2.

  The operating point of the transistor T2 transitions from the class A to the class C by the cutoff pulse signal. Capacitors C1, C3, and C4 are coupling capacitors for removing DC components, respectively. The resistor R1, the capacitor C2, and the Zener diode Z1 constitute a low-pass filter that works only for one-side polarity. The transistors T1 and T2 are field effect transistors such as GaAsFETs. Further, the bias voltage applied to the gate of the field effect transistor T2 is adjusted by the variable resistor R3. In the present embodiment, as an example, the bias voltage applied to the gate of the field effect transistor T2 is set to −1V. The power pulse generator applies a power pulse to the drain of the transistor T2 by the control signal PAON during transmission. In the present embodiment, as an example, the voltage value of the power supply pulse is set to 10V.

  The preamplifier A1 receives a pulsed high frequency signal (RFIN) from the high frequency generator 102, and the AC signal amplified by the preamplifier A1 is input to the gate of the transistor T2 via the capacitor C4. During the period when the power supply pulse applied to the drain of the transistor T2 is 10V (during the high level), the AC signal from the preamplifier A1 is amplified by the transistor T2, and the high frequency signal (RFOUT) is output from the drain of the transistor T2. Is output and transmitted via the circulator 104 and the shared antenna 105.

  Next, the operation of the high-frequency amplifier 103 will be described with reference to FIG. FIG. 3 is a diagram showing signal waveforms at various points in the high-frequency amplifier 103 shown in FIG.

  The control signal (PAON) a input to the power supply pulse generator is a normal amplifier control voltage. The pulse signal (cut-off pulse signal) d is synchronized with the control signal a and the power supply pulse, and is generated at the end of the pulse of the control signal a.

  The control signal a is inverted by the NAND gate N1 to become a signal b. The signal b is further inverted by the NAND gate N2 and inputted to the low-pass filter including the resistor R1 (1 kΩ) and the capacitor C2 (1000 pF) and the anode of the Zener diode Z1. Then, the tail of the drive signal (corresponding to the control signal a) is extended (signal c) by the combination of the Zener diode Z1 and the low-pass filter (resistor R1 and capacitor C2). By taking the logical product of the signal c and the original signal b (NAND gate N3), a pulse signal d for controlling the gate voltage of the transistor T2 is generated.

  The transistor T2, which is the final stage amplifier of the amplifier 103, is normally applied with DC (direct current) -1V as a gate voltage. When the control signal a is at a high level, an RF pulse input (RFIN) is input to the gate of the transistor T2 for pulse transmission, amplified by the transistor T2, and a pulse signal (RFOUT) is output from the drain of the transistor T2. Immediately after the signal a changes to the low level, the gate voltage control pulse signal d is applied to the gate voltage of the transistor T2, and the gate voltage of the transistor T2 is lowered to -2V as shown in the waveform e immediately after the control signal a ends. It is done.

  To summarize the above operation, the gate voltage of the transistor T2 is further swung from −1V to the minus side at the falling edge of the control signal (PAON) a, thereby making the transistor T2 non-operating. When the gate voltage of the transistor T2 returns to the bias value (−1V), it swings to the positive side. At this time, since the drain voltage of the transistor T2 is 0V, no overcurrent flows.

  FIG. 4 shows a waveform e of the gate voltage generated by the circuit of FIG.

  FIG. 4 shows that after the pulse a of the amplifier control voltage falls, the tail of the drain voltage f of the transistor T2 is about 300 ns. On the other hand, the gate voltage e drops to −3 V immediately after the control signal a falls, and the operation state of the final stage amplifier (transistor T2) changes from class A to class C. The noise input level to the receiver was significantly improved by about 13 dB due to the load of this circuit.

  As described above, in the pulse radar according to the present embodiment, the field effect transistor used in the high-frequency amplifier is cut off by the operating point transition (class A to C class operation) instead of the high voltage drain voltage. ing. Focusing on the fact that field-effect transistors generally used in high-power high-frequency amplifiers are used in class A operation, by changing the gate voltage with a low voltage at high speed to achieve class C operation. The amplification function can be significantly reduced. Even if the power supply of the field effect transistor does not drop due to the transition of the operation state from the class A to the class C, the noise output from the amplifier can be cut off by significantly reducing the amplification function.

  Therefore, according to the high-frequency amplifier of the present embodiment, the noise of the high-frequency amplifier is controlled only by controlling the gate voltage with a small voltage and a small amount of current without blocking the drain voltage / current with a high voltage and a large current. The output can be reduced. Therefore, according to the present embodiment, it is possible to relatively easily shorten the measurement limit of the short distance side of the pulse radar. Conventionally, even in a case where a transmission / reception antenna is separated for isolation, transmission / reception is performed. There is a possibility to reduce the size and weight by using a shared antenna.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  For example, in the above embodiment, the pulse radar has been described. However, the present invention is not limited to this, and the present invention can also be applied to a microwave application apparatus or the like.

  The present invention is generally applicable to pulse radars such as in-vehicle radars and aircraft radars.

DESCRIPTION OF SYMBOLS 101 Signal processing part 102 High frequency generation part 103 High frequency amplifier 104 Circulator 105 Transmission / reception common antenna 106 Low noise amplifier 107 Demodulation circuit A1 Preamplifier (Amp)
C1, C2, C3, C4 Capacitors D1, D2,..., Dh Drivers L1, L2 Inductors N1, N2, N3 NAND gates R1, R2, R3 Resistors T1, T2 Transistor Z1 Zener diode

Claims (5)

A field effect transistor that outputs a high-frequency signal from the drain; and
A power pulse generating circuit that generates a power pulse and applies the power pulse to the drain of the field effect transistor;
A gate bias generation circuit for generating a gate bias voltage and applying the gate bias voltage to a gate of the field effect transistor;
A cutoff pulse generation circuit that generates a cutoff pulse signal when the power supply pulse is cut off, and applies the cutoff pulse signal to the gate of the field effect transistor;
The field effect transistor has an operating point that changes from class A to class C according to the cutoff pulse signal. The high-frequency amplifier according to claim 1, wherein
The high-frequency amplifier, wherein the cutoff pulse generation circuit is synchronized with the power supply pulse and generates the cutoff pulse signal when the power supply pulse falls.   A pulse radar comprising the high-frequency amplifier according to claim 1 or 2 at a final stage of a transmission unit. In a high frequency amplifier including a field effect transistor,
A method of blocking an amplification operation and noise output by the field effect transistor by controlling an operating point of the field effect transistor from class A to class C. The method of claim 4, wherein
The high-frequency amplifier is used in a final stage of a transmission unit of a pulse radar.

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