JPS6113652B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic gain control device used in a radio receiver or the like, and an object of the present invention is to provide an excellent automatic gain control device with a simple configuration.

Due to the spread of automobiles and the development of communication systems, recent transmitters and receivers are increasingly being used for in-vehicle applications. I've become unable to be satisfied.

For example, in the U.S. citizen band transceiver, A ₃ and 27MHz band transceivers are used as in-car transceivers.
A ₃ j type modulation, the transmit power is 4W and 4W respectively.
Up to 12W (PEP) is allowed, and the communication distance when communicating using these is several hundred meters.
It is necessary to consider an extremely wide range from long distances such as Km to short distances such as communication between neighboring cars.At the same time, it is necessary to consider the distortion rate, cross-modulation characteristics, etc. even at large inputs of 120 dB or more, as well as high sensitivity. There is a growing demand for a good automatic gain control device with less deterioration.

However, conventional automatic gain control devices that have been commonly used control the operating point of each amplification element that is responsible for signal amplification, and are not only unable to obtain sufficient attenuation characteristics even at large inputs, but also exhibit nonlinear gain control. This method has the disadvantage that unnecessary responses depending on gender are noticeable.

The present invention eliminates the above-mentioned conventional drawbacks, and in addition to improving the distortion characteristics at the time of large input, the present invention also improves the distortion characteristics at the stage before the high frequency amplifier circuit before the signal passes through the steep filter for frequency selection. The structure is designed to prevent as much as possible intermodulation and deterioration of cross-modulation characteristics caused by an increase in nonlinear distortion due to a narrow dynamic range.

In other words, in the present invention, the signal attenuation by the automatic gain control device is zero (or minimal) when the input is small.
When there is a large input signal, the signal is configured to be attenuated significantly depending on the magnitude of the input signal. Therefore, if a conventional automatic gain control device for controlling the amplification degree is used in conjunction with the conventional automatic gain control device for controlling the amplification degree, automatic gain control can be performed using the conventional automatic gain control device for controlling the amplification degree at medium input. Therefore, it can be said that the automatic gain control device of the present invention is the most effective as a delay type automatic gain control device.
In this case, in order to prevent unnecessary responses from occurring due to the nonlinearity of the automatic gain control element itself, it is recommended to use a diode for automatic gain control that has a somewhat longer reverse recovery time so that it does not respond at the frequency used. desirable. In this way, if one with a long reverse recovery time is used, it becomes a mere pure resistance at the frequency used, and nonlinear distortion does not occur. specifically for this purpose
A diode with a PIN structure, which has an intermediate layer called an I layer between the P layer and the N layer called a PIN diode, and has an intentionally longer reverse recovery time has been developed, and the automatic gain control device of the present invention It is very suitable for. However, in experiments conducted by the inventor, it has been confirmed that good results can be obtained even by using a normal switching silicon diode (1S 2473), and therefore the present invention uses a PIN diode as an automatic gain control element. It is not limited to that.

An embodiment of the present invention will be described below with reference to the drawings. In Figure 1, 1 is a high frequency amplification circuit using MOS transistors, 2 is a frequency conversion circuit,
3 is an intermediate frequency amplification circuit, and 4 is a detection circuit.

In the above embodiment, part of the output of the detection circuit 4 is used as an automatic gain control signal, and is used as a high frequency amplifier circuit 1, a frequency conversion circuit 2, and an intermediate frequency amplifier circuit 3.
is applied to. Each of the circuits 1, 2, and 3 constitutes an automatic gain control circuit using normal operating point control. On the other hand, an automatic gain control signal is separately added to the automatic gain control device according to the present invention to constitute a delay type automatic gain control circuit.

The operation of the automatic gain control device of the present invention will be explained below. First, the case of large input will be explained. When a strong input signal is applied from the antenna terminal ANT, the automatic gain control signal appearing at the output terminal of the detection signal 4 increases accordingly, increasing the base current of the transistor 7 via the resistor 5 and diode 6. Here, the resistor 5 and diode 6 are provided for the purpose of setting a delay operation. As the base current of transistor 7 increases, the collector current of transistor 7 is further amplified and increases, causing the forward current of diode 8 to increase. This forward current flows from the +B power supply through the resistor 9 to the diode 8, and the magnitude of the current is controlled by the transistor 7.

As the forward current of the diode 8 increases, the high frequency operating resistance of the diode 8 decreases significantly, and becomes a sufficiently low resistance value. On the other hand, the diode 8 is connected at high frequency to the output side of the antenna tuning circuit by a capacitor 10 and a capacitor 11. Therefore, when the high frequency operating resistance of the diode 8 decreases to a low resistance value, the tuning Q of the antenna tuning circuit decreases.
decreases, transmission loss increases, and the transmission signal to the high frequency amplifier circuit 1 is significantly attenuated. That is, as the detection output increases, the signal from the antenna tuning circuit is attenuated by the automatic gain control signal proportional to the increase.

In addition to the above operations, the collector-emitter impedance of transistor 7 also changes, and the high-frequency impedance decreases as the base current increases. Since this is connected in parallel to the tuning circuit in exactly the same way as a diode in terms of AC, sufficient signal attenuation control can be achieved in conjunction with the signal attenuation effect of the diode.

The series of actions described above operate continuously when a large signal is input, and control is automatically performed to suppress fluctuations in the detection output and obtain a constant detection output.

Next, the cases of small input and medium input will be explained. When the input is small or medium, the detection circuit 4
Since the automatic gain control signal extracted from the input signal is small in proportion to the input signal, it does not exceed the delay operation set value set by the resistor 5 and diode 6, and the base current flowing to the transistor 7 through the resistor 5 and diode 6 is It is zero (or minimal). Therefore, the transistor 7 is in a cut-off state, and the forward current of the diode 8 is also zero (or minimal). In this state, the high-frequency operating resistance of the diode 8 is sufficiently high compared to the resonant impedance of the tuned circuit, and the output resistance of the transistor 7 is also sufficiently large, so that the transmission loss due to Q dump is zero (or minimal). ) and
The output of the antenna tuning circuit is transmitted to the high frequency amplifier circuit 1 under optimal matching conditions.

FIG. 2 shows the input signal level and the relative sensitivity of each automatic gain control circuit for the above embodiment. In Fig. 2, A is the relative sensitivity curve of the automatic gain control circuit of the present invention, B is that of a commonly used automatic gain control circuit based on operating point control of an amplifying element, and C is the overall characteristic of A and B, that is, the above. It is a curve showing the overall characteristics of the example.
In Fig. 2, the input signal level is divided into three regions for convenience, and the small, medium and large input regions are A and B, respectively.
and C.

In FIG. 2, in regions A and B, a normal automatic gain control circuit operates and performs automatic gain control according to the input, and in region C, the automatic gain control circuit according to the present invention mainly operates and performs normal automatic gain control. The circuit will make little contribution. In the embodiment, if the start input signal level of the delay operation of the automatic gain control device of the present invention is set to approximately 80 dB/μV,
Even if the above input signals are received, the automatic gain control device of the present invention can automatically adjust the voltage input to the high frequency amplifier circuit 1 to 80 dB/μV. In conventional automatic gain control circuits, large inputs are directly input to the high-frequency amplifier circuit 1, so when the input exceeds the dynamic range of the high-frequency amplifier circuit 1, the signal waveform is significantly distorted and unnecessary responses due to nonlinear distortion appear. According to the automatic gain control device of the invention, the above drawbacks can be eliminated simply by setting the delay so that the input signal level with the best conditions can be obtained.

Incidentally, FIG. 3 shows the automatic gain control characteristics and input versus distortion characteristics of the above embodiment. In FIG. 3, A is the automatic gain control characteristic, and B is the input versus distortion characteristic, both of which are significantly superior to the conventional characteristics shown by dotted lines.

As is clear from the above embodiments, the automatic gain control device of the present invention includes at least the first automatic gain control circuit that controls the amplification degree of the intermediate frequency amplification stage using a part of the detection signal, and the variable impedance means in the antenna tuning circuit. It consists of a second automatic gain control circuit that is connected in parallel with AC to control the degree of attenuation, and is equipped with means for level-shifting a part of the detected signal, and this level-shifted detected signal is used as the second gain control signal. A delay-type automatic gain control circuit in which a second automatic gain control circuit performs a delay operation according to the input signal strength, wherein the variable impedance means is configured to conduct a delay operation from a voltage source through a resistor, a diode, and between the collector and emitter of a transistor. In addition to grounding, the connection point between the resistor and the diode is AC grounded using a capacitor, the connection point between the diode and the collector of the transistor is connected to the antenna tuning circuit via the capacitor, and the second gain is connected to the base of the transistor. Antenna tuning circuit The transistor controlled by the second gain control signal acts as an AC variable impedance element and also acts as an amplification control element for the DC bias of the diode. As a result, the impedance can be made extremely low, expanding the range of automatic gain control, and the self-rectifying current that occurs in the diode during strong input signals can be bypassed, and sufficient DC bias can always be supplied, reducing waveform distortion. This has the advantage that less automatic gain control can be realized.

[Brief explanation of the drawing]

Fig. 1 is an electrical wiring diagram of an embodiment of the automatic gain control device of the present invention, Fig. 2 is a diagram showing the relative sensitivity characteristics of the above embodiment, and Fig. 3 is a diagram showing the automatic gain control performance and input of the embodiment. FIG. 3 is a diagram showing distortion characteristics. 1... High frequency amplification circuit, 2... Frequency conversion circuit, 3... Intermediate frequency amplification circuit, 4... Detection circuit,
5...Resistor, 6...Diode, 7...Transistor, 8...Diode, 9...Resistance, 10,1
1... Capacitor.

Claims (1)

[Claims] 1 a first automatic gain control circuit that controls the amplification degree of at least the intermediate frequency amplification stage using a part of the detection signal;
It consists of a second automatic gain control circuit that controls the degree of attenuation by connecting a variable impedance means in parallel with the antenna tuning circuit to control the degree of attenuation. A delay type automatic gain control circuit in which a second automatic gain control circuit performs a delay operation according to the input signal strength by using a gain control signal,
The variable impedance means connects a voltage source to a resistor,
In addition to grounding between the collector and emitter of the diode and the transistor, the connection point between the resistor and the diode is AC grounded with a capacitor, and the connection point between the diode and the collector of the transistor is connected to the antenna tuning circuit via the capacitor.
The second gain control signal is applied to the base of the transistor to control the impedance between the collector and emitter of the transistor, and at the same time, the control signal current amplified by the current amplification effect is caused to flow in the forward direction to the diode to control the impedance of the diode. An automatic gain control device characterized in that it is configured as follows.