JP2003318843A - Reception electric field intensity detection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reception electric field intensity detection circuit for shortening transient response time of a reception electric field intensity signal. <P>SOLUTION: The reception electric field intensity detection circuit is provided with gain control amplifier circuits 10a, 10b that amplify an intermediate frequency signal inputted with a gain adjusted by internal control, limiter amplifier circuits 23, 24 that amplify an inputted signal with fixed gain, a wave detection circuit 26 that detects waves of the intermediate frequency signal inputted in the gain control amplifier circuit 10a, a wave detection circuit 29 that detects waves of the input signal in the limiter amplifier circuit 24, a signal addition circuit 30 that generates the reception electric field intensity signal by adding an output signal of the wave detection circuit 26, gain control signals to be outputted from the gain control amplifier circuits 10a, 10b respectively and an output signal of the wave detection circuit 29 together and a low-pass filter circuit 31 that restrict bands of a signal outputted from the signal addition circuit 30 and outputs the reception electric field intensity signal. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a received electric field strength detection circuit having a short transient response time of a received electric field strength signal.

[0002]

2. Description of the Related Art As a receiver circuit used in a receiver such as a mobile communication device, there is a super-heterodyne receiver circuit that converts a high-frequency received signal into an intermediate frequency band and then demodulates it. In a conventional receiver circuit that adopts a limiter amplification method to amplify an intermediate frequency band signal (intermediate frequency signal), an intermediate frequency signal is extracted from each stage of a limiter amplifier circuit having a multi-stage configuration to obtain a received electric field strength signal. A method of detecting the received electric field strength is known.

FIG. 4 shows an example of a configuration related to detection of the received electric field strength of such a receiving circuit. As shown in the figure, the conventional receiving circuit includes a limiter amplifier circuit 21 to 24 that amplifies the intermediate frequency signal input from the terminal 20, and a detection circuit that detects the input signal of each stage of the limiter amplifier circuits 21 to 24. 26-29, and a signal addition circuit 30 for adding the output signals of the detection circuits 26-29 to generate a reception electric field strength signal,
A low pass filter circuit 31 for band limiting the output signal of the signal addition circuit 30 is provided. The detection circuits 26 to 29 are circuits that square-law detect an input signal and output an output signal having a pseudo-logarithmic relationship with the input signal.

The output signal of 24 of the limiter amplifier circuit is taken out from the terminal 25 and output to a circuit in the subsequent stage, for example, a demodulation circuit. Further, the received electric field strength signal that has passed through the low-pass filter circuit 31 is taken out from the terminal 32 and output to a circuit in the subsequent stage, for example, a signal processing circuit.

[0005]

However, in the above conventional receiving circuit, if the attenuation amount of the envelope signal component of the intermediate frequency signal included in the received electric field strength signal is increased, the received electric field strength signal There is a problem that the transient response time becomes long. That is, the envelope signal component of the intermediate frequency signal can be increased by decreasing the cutoff frequency of the low-pass filter 21 or increasing the filter order, but in this case, the step shape of the intermediate frequency signal is increased. Therefore, the transient response time of the received electric field strength signal becomes long with respect to the level change.

Further, the conventional mobile communication device is provided with two systems of antennas, and the receiving circuit of the device compares the received electric field strengths of the signals received by the respective antennas, and the reception electric field strength of the stronger one is received. There is one that employs a so-called diversity reception system in which communication quality is kept good by using a signal. In the antenna switching diversity method in which two systems of antennas are switched for reception with respect to one system of receiving circuit, the shorter the transient response time of the received electric field strength signal with respect to the step change of the signal level at the time of antenna switching, the more the antenna selection becomes. This is preferable because the time required for

However, in the case of a received signal including a baseband modulation component accompanied by envelope fluctuation, in order to properly detect the electric field intensity of the carrier signal component of the signals respectively received by the two antennas, the received electric field intensity It is necessary to attenuate the envelope variation of the baseband modulation signal appearing in the signal to a desired value. This is because if the amount of attenuation of the envelope variation of the baseband modulated signal is not sufficient, the amount of envelope variation is superimposed on the carrier signal component, and the electric field strength of the carrier signal component cannot be detected correctly.

However, as described above, the attenuation amount of the low-pass filter 21 and the transient response time are in a trade-off relationship, and the transient response time becomes long if the attenuation amount is set to a large value, so that the antenna switching diversity. In the conventional receiving circuit adopting the method, there is also a problem that sufficient attenuation may not be obtained in the envelope signal component of the intermediate frequency signal within the desired transient response time.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide a received electric field strength detection circuit capable of shortening the transient response time of a received electric field strength signal.

[0010]

In order to achieve the above object, a received electric field strength detection circuit according to the present invention provides a gain control signal internally generated with a gain so that an output signal linearly operates with respect to an input signal. Gain control amplification means for adjusting and amplifying an input signal with the adjusted gain; first detection means for detecting an input signal of the gain control amplification means; output signal of the first detection means and the gain Reception electric field strength signal generation means for generating a reception electric field strength signal by adding the gain control signal of the control amplification means and band limiting.

Further, in the received electric field strength detection circuit according to the present invention, the gain control amplification means has a variable gain amplification means for amplifying an input signal whose gain is adjusted by the gain control signal, and the variable gain amplification means. Second detection means for detecting the output signal of the second detection means, and integration means for outputting the gain control signal by integrating the output of the second detection means, and the amplitude of the output signal is predetermined by the gain control signal. The gain of the variable gain amplifying means is controlled so as not to exceed the value.

Since the variable gain amplifying means is designed so that the gain changes exponentially with respect to the gain control signal,
As a result, the equivalent time constant of the gain control signal is small, which shortens the transient response time. Since such a gain control signal is included in the signals added by the reception electric field strength signal generating means, it is possible to generate a reception electric field strength signal having a short transient response time. Regarding the attenuation amount of the received electric field intensity signal, not only the time constant due to band limitation but also the time constant of the integrating means can be adjusted, so that the attenuation amount can be increased while keeping the transient response time short.

Further, the received electric field strength detection circuit according to the present invention includes a plurality of amplifying means groups for amplifying the output signal of the gain control amplifying means, and each amplifying means excluding the input signal of the frontmost amplifying means. A third detection circuit group for detecting an input signal, wherein the reception electric field strength signal generation means adds the output signal of the first detection means and the gain control signal of the gain control amplification means to the third detection circuit. Each output signal of the detection circuit group of is also added.

In the received electric field strength detection circuit according to the present invention, the received electric field strength generating means adds the output signal of the first detecting means and the gain control signal of the gain control amplifying means. And band limiting means for band limiting the signals added by the signal adding means.

Further, the mobile communication device according to the present invention is
The reception electric field strength detection circuit according to claim 1, 2, 3 or 4 is provided.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a received electric field strength detection circuit according to the present invention will be described below in detail with reference to the drawings. The reception electric field strength detection circuit of the present embodiment is provided in a superheterodyne type reception circuit, and detects the reception electric field strength by extracting the intermediate frequency signal from each stage of the multistage amplifier circuit to obtain the reception electric field strength. To do. A reception circuit having the reception electric field strength detection circuit is provided in mobile communication devices such as mobile phones and PDAs.

FIG. 1 is a block diagram showing a received electric field strength detection circuit according to an embodiment of the present invention. In the figure, the same parts as those in FIG. 4 (prior art) are designated by the same reference numerals. As shown in FIG. 1, the received electric field strength detection circuit of the present embodiment includes gain control amplification circuits 10a and 10b corresponding to the gain control amplification means of the claims and a limiter amplification circuit 23 corresponding to the amplification means group. 24, a detection circuit 26 corresponding to the first detection means, a detection circuit 29 corresponding to the third detection means group, a signal addition circuit 30 corresponding to the signal addition means, and a low band corresponding to the band limiting means. It is provided with a pass filter circuit 31. The signal addition circuit 30 and the low-pass filter circuit 31 together correspond to the received electric field strength signal generating means in the claims.

The respective constituent elements of the received electric field strength detection circuit of this embodiment will be described below. First, the gain control amplification circuit 10 (10a, 10b) amplifies an input signal with a gain adjusted by internal control, and includes a variable gain amplification circuit 101 corresponding to the variable gain amplification means in the claims. It is composed of a double wave detection circuit 103 corresponding to the second detection means and an integration circuit 105 corresponding to the integration means. The gain control amplifier circuit 10 performs feedback for gain control so that the amplitude of the output signal does not exceed a certain value, that is, it operates linearly with respect to the input signal.

The components of the gain control amplifier circuit 10 will be described below. First, the variable gain amplifier circuit 10
1 is for amplifying the intermediate frequency signal, and its gain is controlled by a gain control signal (described later) output from the integrating circuit 105. The double-wave detection circuit 103 detects the output signal of the variable gain amplification circuit 101.
The integrating circuit 105 integrates the outputs of the both-wave detecting circuit 103 and outputs a gain control signal. The gain control signal is the variable gain amplifying circuit 101 and the signal adding circuit 30.
Is input to both.

The limiter amplifier circuits 23 and 24 amplify the input intermediate frequency signal with a constant gain. Further, the detection circuit 26 is the gain control amplifier circuit 1 of the preceding stage.
The input signal of 0a is detected. The detector circuit 29 detects the input signal of the limiter amplifier circuit 24 in the subsequent stage. Further, the signal addition circuit 30 includes the output signals of the detection circuits 26 and 29 and the gain control amplification circuits 10a and 1a.
The gain control signals output from the integrating circuits 105a and 105b included in 0b are added. The low-pass filter circuit 31 limits the band of the signal output from the signal addition circuit 30. The signal output from the low pass filter circuit 31 is called a received electric field strength signal.

The constituent elements described above except the gain control amplifier circuit 10, that is, the limiter amplifier circuits 23 and 24, the detector circuits 26 and 29, the signal adder circuit 30, and the low-pass filter circuit 31, are the same as those in the prior art. In the received electric field strength detection circuit of the present embodiment, when the intermediate frequency signal obtained by frequency-converting the high frequency signal received by the antenna (not shown) is input from the terminal 20, the gain control amplifier circuit 1
It is taken out from the terminal 25 through the 0a and 10b and the limiter amplifier circuits 23 and 24, and is output to a circuit in the subsequent stage, for example, a demodulation circuit (not shown). Further, the received electric field strength signal that has passed through the low-pass filter circuit 31 is taken out from the terminal 32 and output to a circuit in the subsequent stage, for example, a signal processing circuit.

The transient operation of the gain control amplifier circuit 10 will be described below with reference to FIGS. 2 and 3. Figure 2
FIG. 4 is an explanatory diagram showing characteristics of a received electric field strength signal with respect to an input level of an intermediate frequency signal. The horizontal axis represents the input level of the intermediate frequency signal in decibels (dB), and the vertical axis represents the output level of the received electric field strength signal in linear form. The broken line shown in the figure indicates from the left the level of the output signal of the detection circuit 29, the level of the gain control signal output from the gain control amplification circuit 10a, the level of the gain control signal output from the gain control amplification circuit 10b, and the detection circuit. 26, the solid line represents the output level of a signal (received electric field strength signal) that has been band-limited by the low-pass filter circuit 31 by adding them in the signal addition circuit 30. It shows the linear change characteristic of the output with respect to the change of decibel.

In the gain control amplifier circuit 10, the level of the output signal of the variable gain amplifier circuit 101 is Vo (t),
When the angular frequency of the carrier component of the output signal is ωc, the level Vo (t) of the output signal is represented by Expression (1). Vo (t) = Ao (t) cos (ωct) (1) where Ao (t) is the amplitude of the output signal.

The output signal of the variable gain amplifier circuit 101 is input to the double wave detection circuit 103. The output signal level Vd (t) of the double-wave detection circuit 103 has a linear input / output relationship as shown in Expression (2). Vd (t) = KAo (t) (2)

The output signal of the double wave detection circuit 103 is input to the integration circuit 105 having a frequency characteristic of F (ω). The integrating circuit 105 attenuates the envelope fluctuation component (that is, fluctuation of Ao (t)), and the gain control signal which is its output signal controls the gain of the variable gain amplifying circuit 101. Integrating circuit 105
Is a circuit including a capacitor C and a resistor R, the voltage level V of the output signal of the integrating circuit, that is, the gain control signal.
g (t) is represented by Formula (3). Vg (t) = (1 / τ) ∫ [Vd (t) −Vg (t)] dt (3) However, τ = CR.

From the above equations (1) to (3), the differential equation showing the change in the voltage level Vg (t) of the gain control signal is represented by the equation (4). dVg (t) / dt = (1 / τ) [KAo (t) -Vg (t)] (4) From the equation (4), the equivalent time constant τe is represented by the equation (5). τe = τ / [KAo (t) -Vg (t)] (5)

The variable gain amplifier circuit 101 is generally designed so that the gain changes exponentially with respect to the voltage of the gain control signal. Therefore, in the present embodiment, it is assumed that the gain G (t) of the variable gain amplifier circuit 101 changes as shown in equation (6) with respect to the voltage level Vg (t) of the gain control signal. G (t) = Go × exp [−αVg (t)] (6) From equation (6), when the voltage level Vg (t) of the gain control signal is small, the gain G (t) of the variable gain amplifier circuit 101 is As the voltage level Vg (t) of the gain control signal increases, the gain G (t) decreases.

In the initial state, the gain control amplifier circuit 10
When the input signal level of is changed stepwise from a small state (high gain state) to a large state (rising transient response), KAo (t)> Vg (t) is obtained from the equation (5). The time constant τe becomes smaller. Further, in the initial state, when the input signal level of the gain control amplifier circuit 10 changes stepwise from a high state (low gain state) to a low state (falling transient response), KAo (t) is calculated from the equation (5). Since <Vg (t), the equivalent time constant τe becomes small. Thus, the equivalent time constant τe
Is smaller, the convergence time is shorter.

This relationship is shown in FIG. FIG. 3 is an explanatory diagram showing the transient response characteristic of the gain control signal. The horizontal axis represents time, and the vertical axis represents the level of the gain control signal linearly. The dashed-dotted line shown in the figure shows a step-like transient response of the voltage level of the gain control signal in the case where the integrating circuit 105 includes the capacitor C and the resistor R, and the time constant thereof is τ (= CR). In addition, the broken line shown in FIG.
The time constant in the initial state of the gain control amplifier circuit 10 is τ /
An extension line in the case of [KAo (t) -Vg (t)] is shown. Further, the solid line shown in the figure shows the case where the time constant in the initial state changes from τ / [KAo (t) -Vg (t)] to the characteristic indicated by the dashed line with gain control. . As shown by the solid line in FIG. 3, according to the present embodiment, the equivalent time constant becomes smaller, so the convergence time becomes shorter.

Therefore, the gain control amplifier circuits 10a, 1
In the received electric field strength signal based on the gain control signal from 0b, by adjusting the time constants of the integrating circuits 105a and 105b and the low-pass filter circuit 31, the attenuation amount can be reduced only by the low-pass filter circuit 31. The transient response time can be shortened as compared with the case of increasing it. Similarly, the attenuation amount can be increased as compared with the case where the transient response time is shortened only by the low pass filter circuit 31.

As described above, according to the received electric field strength detection circuit of the present embodiment, the signal added by the signal addition circuit 30 includes the gain control signal having a short transient response time and a large attenuation amount. It is possible to generate a received electric field strength signal having a short transient response time. By incorporating the reception electric field strength detection circuit of the present embodiment having these effects into the reception circuit, it is possible to shorten the transient response time of the reception electric field strength detection circuit and reduce the fluctuation of the envelope fluctuation amount. Further, the base station can be switched in a shorter time while shortening the transient response time of the reception electric field strength detection circuit. Further, it is possible to switch the base station with more accurate received electric field strength while reducing the fluctuation of the envelope fluctuation component of the received electric field strength detection circuit.

The number of stages of the gain control amplifier circuit, the number of stages of the limiter amplifier circuit, and the number of stages of the detection circuit are not limited to those of the present embodiment, but may be different numbers of stages. Further, in the characteristic diagram of the received electric field strength signal output shown in FIG. 2, the output characteristics of each detection circuit and the output characteristics of the gain control signal of each gain control amplifier circuit, which are indicated by broken lines, are all the same. In the case where the range of the input signal level and the slope of the input signal are different from each other, the signal adding circuit 30 performs attenuation or amplification before adding the output of each detection circuit and the output of each gain control signal. The signal level may be adjusted so that the output characteristic of the addition result becomes linear.

[0033]

As described above, according to the received electric field strength detection circuit of the present invention, the variable gain amplification means is designed so that the gain changes exponentially with respect to the gain control signal. As a result, the equivalent time constant of the gain control signal is small, which shortens the transient response time. Since such a gain control signal is included in the signals added by the reception electric field strength signal generating means, it is possible to generate a reception electric field strength signal having a short transient response time. Regarding the attenuation amount of the received electric field intensity signal, not only the time constant due to band limitation but also the time constant of the integrating means can be adjusted, so that the attenuation amount can be increased while keeping the transient response time short.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention,

FIG. 2 is a diagram showing the operating characteristics of FIG.

FIG. 3 is a diagram showing operating characteristics of FIG.

FIG. 4 is a block diagram showing an example of a configuration related to detection of a received electric field strength of a conventional receiving circuit.

[Explanation of symbols]

10a, 10b Gain control amplifier circuit 101a, 101b Variable gain amplifier circuit 103a, 103b double wave detection circuit 105a, 105b integrating circuit 23,24 limiter amplifier circuit 26,29 Detection circuit 30 signal addition circuit 31 Low-pass filter circuit

Claims (5)

[Claims] 1. A gain control amplification means for adjusting a gain by an internally generated gain control signal so that an output signal linearly operates with respect to an input signal, and amplifying the input signal with the adjusted gain, and the gain control. A first detection means for detecting an input signal of the amplification means, and an output signal of the first detection means and a gain control signal of the gain control amplification means are added to perform band limitation to generate a reception electric field strength signal. A received electric field strength detection circuit, comprising: 2. The gain control amplification means includes a variable gain amplification means for amplifying an input signal, the gain of which is adjusted by the gain control signal, and a second detection means for detecting an output signal of the variable gain amplification means. And an integrating means for integrating the output of the second detecting means and outputting a gain control signal, wherein the gain control signal prevents the amplitude of the output signal from exceeding a predetermined value. The received electric field strength detection circuit according to claim 1, wherein the gain is controlled. 3. An amplifying means group having a plurality of stages for amplifying an output signal of the gain control amplifying means, and a third detecting circuit group for detecting an input signal of each amplifying means except an input signal of the amplifying means of the front stage. And the reception electric field intensity signal generation means adds each output signal of the third detection circuit group in addition to the output signal of the first detection means and the gain control signal of the gain control amplification means. 3. The received electric field strength detection circuit according to claim 1 or 2. 4. The reception electric field strength generation means includes a signal addition means for adding an output signal of the first detection means and a gain control signal of the gain control amplification means, and a signal added by the signal addition means. 4. The received electric field strength detection circuit according to claim 1, 2 or 3, further comprising: band limiting means for band limiting. 5. A mobile communication device comprising the received electric field strength detection circuit according to claim 1, 2, 3, or 4.