JP3713206B2 - Automatic gain control circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic gain control circuit used for a front end of a digital terrestrial broadcast receiver.
[0002]
[Prior art]
A front end including a conventional automatic gain control circuit used for a front end of a digital terrestrial broadcast receiver is configured as shown in FIG. For example, the signals of the same channel received by four antennas at different positions are supplied to the variable gain amplifiers 1, 4, 7, and 10 via the high frequency selection circuits, respectively, and are amplified. The amplified outputs of 4, 7, and 10 are supplied to the variable gain amplifiers 2, 5, 8, and 11 for amplification, and the amplified outputs of the variable gain amplifiers 2, 5, 8, and 11 are tracked by the tracking filters 3, 6, 9, 12 is separately supplied to perform band limitation mainly for the purpose of image frequency removal, and outputs band-limited by the tracking filters 3, 6, 9, and 12 are supplied to the synthesizer 13 for synthesis. The output is frequency-converted to a first intermediate frequency by a frequency converter comprising a mixer 14 and a local oscillator 15, and the frequency-converted first intermediate frequency signal is supplied to the detector 17 to be detected, and the detection output current is detected. Was the first automatic gain control voltage is performed an automatic gain control for controlling the gain of the variable gain amplifier 1, 4, 7, 10 based on the voltage.
[0003]
Further, the first intermediate frequency signal is supplied to the band pass filter 21 to perform band limitation such as removal of adjacent channels and high frequency components generated by frequency conversion, and the output of the band pass filter 21 is supplied to the amplifier 22. Then, the amplified output from the amplifier 22 is supplied to the band pass filter 23 for band limitation, and the output from the band pass filter 23 is supplied to the variable gain amplifier 24 for amplification, and then the mixer 25 and the local oscillator. The second intermediate frequency signal frequency-converted to the second intermediate frequency by the frequency converter composed of 26, and supplied to the detection circuit 27 for detection, and the detection output voltage as the second automatic gain control voltage, Automatic gain control is performed to control the gain of the variable gain amplifier 24 based on the voltage.
[0004]
Furthermore, the second intermediate frequency signal is guided to the demodulator 40 and demodulated. On the other hand, the first automatic gain control voltage is led to the A / D converter 18 and converted into a digital signal, and the second automatic gain control voltage is similarly led to the A / D converter 28 and converted into a digital signal. The conversion outputs of the D converters 18 and 28 are also supplied to the demodulator 40, and the demodulator 40 determines the level of the input signal from the conversion outputs of the A / D converters 18 and 28, and the determination output is D / A converted. Is supplied to a control circuit 41 including a converter and converted into an analog signal, and the gains of the variable gain amplifiers 2, 5, 8, and 11 are sequentially changed independently in the period of the guard interval by an analog voltage based on the determination output. Diversity reception is performed by performing automatic gain control.
[0005]
In the case of a digital terrestrial broadcast receiver, unlike a digital satellite broadcast receiver, the D / U ratio (desired to undesired power ratio) between adjacent channels and adjacent adjacent channels is large, so sensitivity reduction when the D / U ratio is large And third-order distortion becomes a problem. Also, since the modulation method is OFDM, the influence of distortion is greater than that of mere PSK modulation, so it is difficult to make the front-end automatic gain control loop in a digital terrestrial broadcast receiver into one loop. As shown in FIG. 5, separate automatic gain control loops are formed before and after the band limitation of the first intermediate frequency signal to suppress the occurrence of distortion due to the first-stage amplifier and mixer.
[0006]
[Problems to be solved by the invention]
Since there are two automatic gain control loops for the reasons described above, there are two automatic gain control voltages for detecting the input signal level used for diversity. The digital signal is converted by an A / D converter, and the input signal level is determined by a demodulator at the subsequent stage.
[0007]
As described above, the conventional front-end automatic gain control circuit in the digital terrestrial broadcasting receiver requires two A / D converters to detect the input signal level on the demodulator side. was there.
[0008]
An object of the present invention is to provide an automatic gain control circuit that requires only one A / D converter for detecting an input signal level on the demodulator side.
[0009]
[Means for Solving the Problems]
The automatic gain control circuit according to the present invention uses the gain of the first stage variable gain amplifier that amplifies signals of the same channel output from a plurality of antennas provided at different positions, and the first intermediate frequency signal before band limitation. Controlled by the detected first automatic gain control voltage,
A gain of a variable gain amplifier that amplifies the first intermediate frequency signal after band limitation is controlled by a second automatic gain control voltage obtained by detecting a second intermediate frequency signal obtained by frequency-converting the first intermediate frequency signal after band limitation;
The (gain / automatic gain control voltage) is set by computing means for making the (gain / automatic gain control voltage) of the first automatic gain control voltage and the (gain / automatic gain control voltage) of the second automatic gain control voltage the same. The input level to the demodulator is determined by the voltage obtained by adding the outputs of the first and second automatic gain control circuits that are the same,
Based on the determined input level, the gain of the variable gain amplifier for diversity is connected to the first-stage variable gain amplifiers respectively, and the output voltage is combined and the combined output is frequency converted into the first intermediate frequency signal. In addition, the control is performed independently and independently.
[0010]
According to the automatic gain control circuit of the present invention, the gain of the first stage variable gain amplifier is controlled by the first automatic gain control voltage, and the gain of the variable gain amplifier that amplifies the first intermediate frequency signal after band limitation is the second automatic gain control voltage. The input level is determined based on a voltage obtained by combining the first automatic gain control voltage and the second automatic gain control voltage, which are controlled by the gain control voltage and the same (gain / automatic gain control voltage) is set by the arithmetic means, Based on the determined input level, the gain of the variable gain amplifier for diversity is controlled. Therefore, the input level to the demodulator is determined by the voltage obtained by adding the outputs of the first and second automatic gain control circuits having the same (gain / automatic gain control voltage). Therefore, only one A / D converter for A / D converting the signal for this purpose is sufficient.
[0011]
In the automatic gain control circuit according to the present invention, a voltage obtained by adding the outputs of the first and second automatic gain control circuits having the same (gain / automatic gain control voltage) is compared with a threshold value and received based on the comparison result. You may provide the input level determination circuit which determines whether it is a possible level.
[0012]
When the automatic gain control circuit according to the present invention includes the input level determination circuit, the input level can be determined based on the output of the input level determination circuit.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
An automatic gain control circuit according to the present invention will be described below with reference to an embodiment.
[0014]
FIG. 1 is a block diagram showing a configuration of a front end in a digital terrestrial broadcast receiver including an automatic gain control circuit according to an embodiment of the present invention.
[0015]
In the automatic gain control circuit according to the present invention, the same components as those in the automatic gain control circuit shown in FIG. 4 are denoted by the same reference numerals, and the description of the same components is omitted to avoid duplication.
[0016]
The automatic gain control circuit according to the embodiment of the present invention multiplies the detection output voltage of the detection circuit 17, that is, the first automatic gain control voltage, to the output voltages of the multiplier 20-1 and the multiplier 20-1, and adds an offset. Is supplied to the arithmetic circuit 20 including the arithmetic unit 20-2 for performing the calculation, and the detection output voltage of the detection circuit 28, that is, the second automatic gain control voltage, is output from the multiplier 42-1 and the multiplier 42-1. Is supplied to an arithmetic circuit 42 including an arithmetic unit 42-2 for performing multiplication and offset addition, and an output voltage of the arithmetic circuit 20 and an output voltage of the arithmetic circuit 42 are added by an adder circuit 43, and an adder circuit The output voltage of 43 is supplied to the A / D converter 44 and converted into a digital signal. The digital signal converted by the A / D converter 44 is supplied to the demodulator 40, and the output of the A / D converter 44 is output. Based on demodulator 40 It is so as to determine the level of Oite input signal.
[0017]
The multiplier 20-1 multiplies the output voltage of the detection circuit 17 by a multiplication coefficient (1 / X), and the arithmetic unit 20-2 multiplies the output voltage of the multiplier 20-1 by a multiplication coefficient B and adds an offset value. The multiplier 42-1 multiplies the output voltage of the detection circuit 27 by the multiplication coefficient (1 / Y), and the arithmetic unit 42-2 multiplies the output voltage of the multiplier 40-1 by the multiplication coefficient A and the offset. The value is added, the multiplication coefficient (1 / X), B, (1 / Y), A and the offset value are selected, and the gain / automatic gain control voltage (dB / V) based on the output voltage of the arithmetic circuit 20 And the gain / automatic gain control voltage (dB / V) by the output voltage of the arithmetic circuit 42 are set to be the same.
[0018]
The multiplier 20-1, the computing unit 20-2, the multiplier 42-1, and the computing unit 42-2 can be configured by resistance voltage dividers, and the multiplier 20-1 and the computing unit 20-2 are first automatic. An arithmetic unit that multiplies the gain control voltage by a multiplication coefficient (B / X) and adds an offset value may be used. The multiplier 42-1 and the arithmetic unit 42-2 multiply the second automatic gain control voltage. An arithmetic unit that multiplies the coefficient (A / Y) and adds an offset value can also be used.
[0019]
The output voltage of the arithmetic circuit 20 and the output voltage of the arithmetic circuit 42 are added by an adder circuit 43 comprising an operational amplifier, A / D converted by an A / D converter 44, and supplied to a demodulator 40. In the adder circuit 43, the gain is set so that the output voltage matches the input range of the A / D converter 44.
[0020]
The automatic gain control voltage-gain characteristic of the automatic gain control circuit including the detector 17 for controlling the gain of the variable gain amplifiers 1, 4, 7, 10 is generally as shown by the straight line a in FIG. The automatic gain control voltage-gain characteristic of the automatic gain control circuit including the detector 27 for controlling the gain of the variable gain amplifier 24 is generally as shown by the straight line b in FIG. The voltage (dB / V) is different between the automatic gain control circuit including the detector 17 and the automatic gain control circuit including the detector 27.
[0021]
Therefore, as described above, the output voltage-gain characteristic of the arithmetic circuit 20 and the output voltage-gain characteristic of the arithmetic circuit 42 are equalized by the calculation by the arithmetic circuits 20 and 42, and the output voltage-gain characteristic of the adder circuit 43 is As shown in FIG. 2 (b), the input level is determined based on the output voltage of the adder circuit 43, and the gains of the variable gain amplifiers 2, 5, 8, 11 are independent based on the determined input level. And controlled diversity. By doing so, the total gain of the front end can be expressed in a substantially linear form, and the automatic gain control voltage for diversity can be made one.
[0022]
According to the automatic gain control circuit according to the embodiment of the present invention described above, the automatic voltage control voltage for diversity can be made one, and the demodulator 40 can easily calculate the input level for diversity. Become.
[0023]
In the above description, the case where the arithmetic circuits 20 and 42 are provided in order to match the gain / automatic gain control voltage (dB / V) has been described. However, any one of the arithmetic circuits may be used.
[0024]
Next, an example in which an input level determination circuit is provided in one embodiment of the present invention will be described.
[0025]
FIG. 3 is a block diagram showing a configuration when an input level determination circuit is provided in the front end shown in FIG.
[0026]
As shown in FIG. 3, the threshold data is converted into an analog voltage by the D / A converter 45-1, the threshold converted to the analog voltage and the output voltage of the adder circuit 43 are compared by the comparator 45-2, An input level determination circuit 45 for sending a comparison output as an input level determination output is provided in the front end shown in FIG.
[0027]
Therefore, by setting the threshold value to a value corresponding to the receivable input level, the current input level can be received based on whether the output voltage of the adder circuit 43 exceeds the threshold value or less than the threshold value. It can be determined whether or not the input level.
[0028]
【The invention's effect】
As described above, according to the automatic gain control circuit of the present invention, the demodulator is supplied with the voltage obtained by adding the outputs of the first and second automatic gain control circuits having the same (gain / automatic gain control voltage). Since the input level is determined, the effect that only one A / D converter is required to perform A / D conversion on the signal for determining the input level is obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a front end in a digital terrestrial broadcast receiver including an automatic gain control circuit according to an embodiment of the present invention.
FIG. 2 is an automatic gain control characteristic diagram for explaining the operation of the automatic gain control circuit according to the embodiment of the present invention.
FIG. 3 is a block diagram when an input level determination circuit is added to the front end shown in FIG. 1;
FIG. 4 is a block diagram showing a configuration of a front end in a digital terrestrial broadcast receiver including a conventional automatic gain control circuit.
[Explanation of symbols]
1, 2, 4, 5, 7, 8, 10, 11, and 24 Variable gain amplifier 13 Synthesizer 14 and 25 Mixer 15 and 26 Local oscillator 17 and 27 Detection circuit 20 and 42 Operation circuit 40 Demodulator 43 Addition circuit 45 Input level judgment circuit

Claims (2)

The gain of the first stage variable gain amplifier that amplifies signals of the same channel output from a plurality of antennas provided at different positions is controlled by a first automatic gain control voltage obtained by detecting the first intermediate frequency signal before band limitation. And
A gain of a variable gain amplifier that amplifies the first intermediate frequency signal after band limitation is controlled by a second automatic gain control voltage obtained by detecting a second intermediate frequency signal obtained by frequency-converting the first intermediate frequency signal after band limitation;
The (gain / automatic gain control voltage) is set by computing means for making the (gain / automatic gain control voltage) of the first automatic gain control voltage and (gain / automatic gain control voltage) of the second automatic gain control voltage the same. The input level to the demodulator is determined by the voltage obtained by adding the outputs of the first and second automatic gain control circuits that are the same,
Based on the determined input level, the gain of the variable gain amplifier for diversity is connected to the first-stage variable gain amplifiers respectively, and the output voltage is combined and the combined output is frequency converted into the first intermediate frequency signal. An automatic gain control circuit characterized by being controlled independently and independently for each. 2. The automatic gain control circuit according to claim 1, wherein a voltage obtained by adding the outputs of the first and second automatic gain control circuits having the same (gain / automatic gain control voltage) is compared with a threshold value and based on the comparison result. An automatic gain control circuit comprising an input level determination circuit for determining whether or not the level is a receivable level.

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