JP2009065510A - Amplifying apparatus with gain control function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an amplifying apparatus with a gain control function, having more simplified circuit configuration and with fewer number of components. <P>SOLUTION: The amplifying apparatus 1 consists of an amplifying circuit 10 and a gain control circuit 20 that are connected in series. The gain control circuit 20 includes an input-stage transformer 21 which boosts an inputted FM signal αS<SB>FM</SB>and outputs it, a voltage limiter circuit 23 which attenuates the FM signal αS<SB>FM</SB>by an attenuation amount c, and an output stage transformer 25 which steps-down a frequency modulation signal cαS<SB>FM</SB>output from the voltage limiter circuit 23 and outputs it. The voltage limiter circuit 23 has a diode 23-1, which is connected to the output terminal of the input stage transformer and causes more current to flow therein the higher the voltage level of the FM signal αS<SB>FM</SB>becomes; and a diode 23-2 which is connected in parallel with the diode 23-1 and in the reverse direction and causes more current to flow therein as the higher the voltage level of the FM signal αS<SB>FM</SB>becomes. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an amplifying apparatus with a gain control function for controlling a power level of a high frequency signal so as not to exceed a predetermined level when the high frequency signal is amplified and output.

  In AM / FM radio, mobile phones, and the like, the reception level varies depending on the distance from the broadcasting station (base station), fading, and the like. For example, in AM / FM radio and the like, the reception level may be strong in a strong electric field zone such as around a broadcasting station. If the reception level becomes excessively strong, the amplifier circuit is saturated, causing phenomena such as intermodulation distortion and intermodulation distortion. This is not preferable because it causes a phenomenon such as making the radio difficult to hear. Also, a reception level that is too low is also not preferable because it degrades the signal-to-noise ratio SNR of the received signal.

  In general, as a countermeasure against fluctuations in reception level in a wireless terminal, an amplifying apparatus to which a gain control function (for example, AGC: Automatic Gain Control) is added may be used. In this way, the amplifying apparatus to which the gain control function is added controls the power level of the high frequency signal output from the amplifying circuit in addition to the amplifying circuit that amplifies and outputs the input high frequency signal. A gain control circuit is provided (Non-Patent Document 1).

Yukihiko Miyamoto “Design and Implementation of High Frequency Circuits” Japan Broadcasting Publishing Association, Chapter 7-Automatic Gain Control Circuit

  There are roughly two types of amplifying device configurations to which a gain control function is added. That is, the gain of the amplifying circuit is changed by changing the operating point of the amplifying element according to the strength of the input high-frequency signal, and a variable attenuator is constituted by a PIN diode or the like to be input to the amplifying element ( Or a configuration for attenuating a high-frequency signal (output from the amplifying element).

  Both of these two types of amplifying devices have a function of detecting the signal level of a high-frequency signal (for example, converting the reception level into a detection voltage), a function of amplifying the detection voltage, and the magnitude of the detection voltage. A function for controlling the gain and the attenuation is required.

  For this reason, the conventional amplification device to which the gain control function is added has a tendency that the circuit configuration of the amplification device itself is complicated. More specifically, there has been a tendency to increase the number of parts, and to increase the mounting space and manufacturing cost for communication equipment.

  Therefore, the conventional amplifying device to which the gain control function is added needs some countermeasures against the problems of an increase in the number of components and an accompanying increase in the mounting space and manufacturing cost in communication equipment. An object of the present invention is to solve the above-described problems, and to realize an amplifying apparatus with a gain control function in which the number of parts is reduced with a simpler circuit configuration.

  The present invention includes an amplification circuit that amplifies and outputs an input high-frequency signal, and a gain control circuit that controls a power level of the high-frequency signal output from the amplification circuit so as not to exceed a predetermined level. An amplification device with a control function, wherein the high frequency signal is a frequency modulation signal, the amplification circuit and the gain control circuit are connected in series, and the gain control circuit boosts the input frequency modulation signal. An input stage transformer for output and a first diode through which current flows as the voltage level of the frequency modulation signal is increased and connected between the output terminals of the input stage transformer and the first diode in parallel and in opposite directions And a voltage limiter circuit having a second diode through which current flows as the voltage level of the frequency modulation signal increases, and the voltage limiter circuit An output stage transformer frequency modulation signal by stepping down output, which is characterized in that it comprises a.

  According to the present invention, it is possible to realize an amplifying apparatus with a gain control function in which the number of parts is reduced with a simpler circuit configuration.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of an amplifying apparatus 1 with a gain control function according to the present embodiment. Note that the amplifying apparatus with a gain control function shown in the present embodiment is externally connected to the FM radio. Hereinafter, the configuration of the amplifying apparatus 1 shown in FIG. 1 will be described in detail.

The amplifying apparatus 1 shown in FIG. 1 includes an amplifying circuit 10 and a gain control circuit 20. Amplifier circuit 10, an antenna is input FM signal S _FM received (not shown), which was amplified with a predetermined gain alpha, a circuit for outputting the amplified FM signal [alpha] S _FM. As described above, the antenna FM signal S _FM received (not shown) is a value that varies. The gain α of the amplifier circuit 10 is a constant value (however, only in the linear region).

Next, the configuration of the gain control circuit 20 will be described. First, an outline will be described. The gain control circuit 20 is connected in series with the amplifier circuit 10 described above. The gain control circuit 20 is a circuit that controls the FM signal αS _FM output from the amplifier circuit 10 so as not to exceed a predetermined level (attenuates by an attenuation amount c) and outputs the FM signal cαS _FM . The attenuation amount c is a value that satisfies 0 <c ≦ 1. As described later, the gain control circuit 20 is smaller when the FM signal S _FM larger increases when FM signal S _FM is small. Thus, the FM signal cαS _FM output from the gain control circuit 20 is controlled so as not to exceed a predetermined level.

Details of the configuration of the gain control circuit 20 will be described. The gain control circuit 20 includes an input stage transformer 21, a voltage limiter circuit 23, and an output stage transformer 25. The input stage transformer 21 includes an input side winding 21-1 and an output side winding 21-2. Further, the input-side winding 21-1 is connected in series with the amplifier circuit 10 described above. The output side winding 21-2 has more turns than the input side winding 21-1, and is electromagnetically coupled to the input side winding 21-1. That is, the input stage transformer 21, the FM signal [alpha] S _FM output from the amplifier circuit 10 is applied to the input winding 21-1, and outputs the boosted it from the output side winding 21-2.

The voltage limiter circuit 23 includes diodes 23-1 and 23-2. Diode 23-1 is connected between the output terminal of the input stage transformer 21, as (in the forward direction) the voltage level of the boosted FM signal [alpha] S _FM becomes higher (forward) current flows. The diode 23-2 is connected so as to be parallel and its rectifying direction is the opposite direction to the diodes 23-1, the boosted FM signal [alpha] S _FM (the forward direction) as the voltage level becomes higher (forward) Current flows.

The output stage transformer 25 includes an input side winding 25-1 and an output side winding 25-2. Further, the output side winding 25-2 is connected to a subsequent stage amplifier circuit (not shown). The input side winding 25-1 has more turns than the output side winding 25-2 and is electromagnetically coupled to the output side winding 25-2. That is, the output stage transformer 25, when the FM signal [alpha] S _FM output from the voltage limiter circuit 23 is applied to the input winding 25-1, and outputs the step-down it from the output side winding 25-2. If the winding ratio of the input stage transformer 21 (input side winding 21-1 to output side winding 21-2) is 1: N (N> 0), the winding ratio of the output stage transformer 25 (input side The winding 25-1 vs. output side winding 25-2) is preferably N: 1.

Next, the operation of the amplifying apparatus 1 shown in FIG. 1 will be described. As described above, the amplifier circuit 10 amplifies the input FM signal _SFM with a predetermined gain α and outputs it. The gain control circuit 20 controls the FM signal αS _FM output from the amplifier circuit 10 so as not to exceed a predetermined level (attenuates by the attenuation amount c) and outputs the FM signal cαS _FM .

As described above, the gain control circuit 20 via an input stage transformer 21 and outputs the boosting an FM signal [alpha] S _FM. Here, when the FM signal S _FM input to the amplifier circuit 10 is small, the FM signal αS _FM output from the amplifier circuit 10 also decreases. Thus, when the FM signal [alpha] S _FM output from the amplification circuit 10 is small, a forward voltage applied to each of the diodes 23-1 and 23-2 of the voltage limiter circuit 23 is also reduced.

Therefore, no current flows through each of the diodes 23-1 and 23-2 of the voltage limiter circuit 23 (or very small even if current flows), and the voltage limiter circuit 23 is opened from the input stage transformer 21. (Or high impedance state). That is, the FM signal cαS _FM output from the voltage limiter circuit 23 is applied to the output stage transformer 25 without being attenuated (or slightly attenuated) (that is, c≈1).

Further, the output stage transformer 25 boosts and outputs the applied FM signal Shiarufaesu _FM. Therefore, as described above (assuming that the turns ratio of the input stage transformer 21 is 1: N and the turns ratio of the output stage transformer 25 is N: 1), the gain control circuit 20 outputs the FM output from the amplifier circuit 10. The signal cαS _FM (= αS _FM ) is output as it is.

On the other hand, when the FM signal S _FM input to the amplifier circuit 10 is large, the FM signal αS _FM output from the amplifier circuit 10 also increases. Thus, when the FM signal [alpha] S _FM larger output from the amplification circuit 10, a forward voltage applied to each of the diodes 23-1 and 23-2 of the voltage limiter circuit 23 also becomes large.

Therefore, a current flows through each of the diodes 23-1 and 23-2 of the voltage limiter circuit 23, and from the input stage transformer 21, the voltage limiter circuit 23 is connected in parallel with a resistor that consumes the current. Can be considered. That is, the FM signal cαS _FM output from the voltage limiter circuit 23 is attenuated by the amount of current consumed and applied to the output stage transformer 25 (ie, c <1). The FM signal cαS _FM attenuated in this way is stepped down by the output stage transformer 25 and output.

Further, the diodes 23-1 and 23-2, as the forward voltage increases (i.e. as the FM signal [alpha] S _FM larger output from the amplification circuit 10), consumes a current flowing forward current. Therefore, the amplifying apparatus 1 shown in FIG. 1 can perform control so that the power level does not exceed a predetermined level when the FM signal _SFM is amplified.

Note that the signal waveform of the FM signal cαS _FM via the gain control circuit 20 is distorted (due to the non-linearity of the diodes 23-1 and 23-2). However, in the case of the FM signal, the modulation signal is generated due to frequency density. Therefore, there is no particular problem during demodulation.

  A voltage boosted by the input stage transformer 21 is applied to the voltage limiter 23. For this reason, the diodes 23-1 and 23-2 can operate even with a relatively low voltage signal. Therefore, the cost of the diode itself can be reduced, and the operating range can be widened with respect to the FM signal level.

  Furthermore, the amplifier circuit 10 and the gain control circuit 20 may be connected in series. For example, the gain control circuit 20 may be provided in the previous stage of the amplifier circuit 10, or the gain is provided in both the front and rear stages of the amplifier circuit 10. A control circuit 20 may be provided.

  As described above, in the amplification device with a gain control function according to the present embodiment, the amplification circuit and the gain control circuit are connected in series, and the gain control circuit boosts and outputs the input frequency modulation signal. In addition, the voltage level of the frequency modulation signal is connected between the output terminals of the input stage transformer and connected in parallel and in the opposite direction to the first diode through which current flows as the voltage level of the frequency modulation signal increases. A voltage limiter circuit having a second diode through which current flows as it increases, and an output stage transformer that steps down and outputs a frequency modulation signal output from the voltage limiter circuit. Thereby, the amplification device with a gain control function according to the present embodiment can be configured to have a simpler circuit configuration and a reduced number of parts.

  Needless to say, the amplifying apparatus with a gain control function according to the present embodiment is not limited to the FM signal but can be applied to other frequency modulation signals (for example, FSK). Needless to say, the amplifying apparatus with a gain control function according to the present embodiment can also be applied to communication devices other than FM radios (for example, FM radios and mobile phones).

It is a figure which shows the circuit structure of the amplifier with a gain control function which concerns on this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Amplifying device, 10 Amplifying circuit, 20 Gain control circuit, 21 Input stage transformer, 23 Voltage limiter circuit, 25 Output stage transformer

Claims (1)

An amplifier circuit for amplifying and outputting the input high frequency signal;
A gain control circuit for controlling the power level of the high-frequency signal output from the amplifier circuit so as not to exceed a predetermined level;
An amplifying device with a gain control function comprising:
The high frequency signal is a frequency modulated signal;
The amplifier circuit and the gain control circuit are connected in series,
The gain control circuit includes:
An input stage transformer that boosts and outputs an input frequency modulation signal; and
The voltage of the frequency modulation signal connected between the output terminals of the input stage transformer and connected in parallel and in the opposite direction to the first diode through which current flows as the voltage level of the frequency modulation signal increases. A voltage limiter circuit having a second diode through which current flows as the level increases;
An output stage transformer for stepping down and outputting the frequency modulation signal output from the voltage limiter circuit;
An amplifying apparatus with a gain control function.

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