JP2002214259A - Frequency analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency analyzer which can extremely restrict noises generated by sufficiently utilizing the dynamic range of an A/D converter. SOLUTION: In the frequency analyzer, the gain of an automatic gain control amplifier 1 is controlled so as to restrict output noise components of the A/D convertor 3 as generated in proportion to the respective squares of an input voltage and a frequency of the A/D convertor 3. Based on the frequency spectrum information, factors contributing to the output noise components of frequency components and totalled covering the frequency components to be defined as an output noise control value. The gain of the automatic gain control amplifier 1 is controlled so as to hold the output noise control value below a specified reference value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a frequency analyzer for analyzing a frequency spectrum component of an analog signal.

[0002]

2. Description of the Related Art Hitherto, a frequency analyzer such as a spectrum analyzer or an FFT analyzer has been used to check a frequency component of an analog signal. For example, when a predetermined analog signal is input to an FFT analyzer, the input signal is subjected to high-speed digital processing and frequency components included in the signal are extracted. The power value (voltage value) and frequency for each frequency component can be read directly on the display screen of the frequency analyzer.

FIG. 2 shows an example of a conventional frequency analyzer. As shown in FIG. 2, the conventional frequency analyzer includes an AGC amplifier 1 for amplifying an analog signal to a predetermined voltage, a low-pass filter 2 for removing harmonic components of the analog signal amplified by the AGC amplifier 1, An A / D converter 3 for sampling an analog signal filtered by the low-pass filter 2 and converting the analog signal into a digital signal;
A clock oscillator 4 for supplying a sampling clock to the D converter 3 and an input signal of the A / D converter 3 are detected based on a digital signal output from the A / D converter 3 and the AGC is performed.
An AGC control unit 5 for controlling the gain of the amplifier 1 and an FFT for performing a fast Fourier transform process on the digital signal supplied from the A / D converter 3 and outputting predetermined frequency spectrum information
(Fast Fourier Transform) means 6.

The conventional frequency analyzer shown in FIG. 2 operates as follows. First, when no signal is input to the AGC amplifier 1, the analog signal is not supplied to the A / D converter 3, so that the output of the A / D converter 3 is also turned off. Therefore, the AGC control unit 5 controls the AGC amplifier 1 to increase the gain, and the gain is maintained at the maximum gain. Therefore, when an analog signal is input, the AGC amplifier 1 amplifies the signal at the maximum gain and supplies the signal to the A / D converter 3 via the low-pass filter 2. The A / D converter 3 converts this into a digital signal and supplies it to the AGC controller 5. The AGC control unit 5 detects the digital signal and
AGC until the input voltage of the / D converter 3 converges to a predetermined value
Control is continued to reduce the gain of the amplifier 1, and finally the gain of the AGC amplifier 1 converges to a predetermined gain according to the voltage value of the input signal. The digital signal output from the A / D converter 3 is processed by the FFT means to output desired frequency spectrum information, which is displayed on a predetermined display screen.

[0005]

However, the conventional frequency analyzer has the following problems. That is, it is preferable to set the input voltage value of the A / D converter 3 as large as possible within the dynamic range of the A / D converter. However, if the input voltage value of the A / D converter 3 is set too large, a problem occurs that the output noise of the A / D converter 3 sharply increases.

Generally, the output noise N of the A / D converter is the noise Na due to the aperture jitter of the sampling clock.
j, differential nonlinear noise Nd, and thermal noise Nq including quantization noise are represented by the following equation. N = Naj + Nd + Nq (1) FIG. 3 shows a change in power of noise N output from a general A / D converter. As shown in FIG. 3, when the input voltage value of the A / D converter is small, the noise N output from the A / D converter is almost constant and the differential nonlinear noise Nd
And thermal noise Nq including quantization noise dominantly contribute. However, when the input voltage increases, Naj predominantly contributes, and the output noise N sharply increases.

Here, it is known that the noise component Naj caused by the aperture jitter of the sampling clock is represented by the following equation. Naj = 2 (πfinAσ) ² (2) (fin: frequency of input signal, A: amplitude voltage of input signal, σ: aperture jitter amount of sampling clock)

Accordingly, since Naj is proportional to the frequency of the input signal and the square of the amplitude voltage, the maximum frequency is assumed for the input signal of the A / D converter, and the input voltage of the A / D converter is set to A as much as possible.
A point close to the point is set, and the output voltage of the AGC amplifier is set. However, the point A changes when the frequency is different, and when a signal having a frequency lower than the assumed maximum frequency is input, the point where Naj becomes dominant changes from the point A to the point A ′. The dynamic range of the A / D converter cannot be fully utilized. Therefore,
This is disadvantageous when dealing with very low level signals.

When the frequency of the sampling clock of the A / D converter is increased to improve the output noise N of the A / D converter, the total power value of the quantization noise Nq does not change, but is shown in FIG. As described above, the noise power density (noise power per 1 Hz) changes, and it is possible to equivalently reduce the quantization noise Nq. However, Naj cannot be suppressed only by increasing the sampling clock, and if the frequency of the sampling clock is increased, a high-speed A / D converter is required, and power consumption may increase. It is hardly an effective means.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and it is an object of the present invention to optimize an input voltage of an A / D converter in accordance with a frequency of an input signal and suppress output noise of the A / D converter. It is an object of the present invention to provide a frequency analysis device that can perform the analysis.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the present invention, there is provided an automatic gain control amplifier for amplifying an analog signal to a predetermined voltage, and the automatic gain control amplifier supplies the automatic gain control amplifier. An A / D converter that samples a signal of a predetermined voltage and converts the signal into a digital signal; and processes a digital signal output from the A / D converter to convert the frequency and power of a frequency component included in the analog signal into frequency spectrum information. A frequency analysis device provided with a Fourier transforming means for outputting the output noise component of the A / D converter, which is generated in proportion to the square of each of the input voltage and the frequency of the A / D converter. An element that controls the gain of the automatic gain control amplifier and that contributes to the output noise component of the frequency component based on the frequency spectrum information. The output noise control value is obtained by summing the elements over all frequency components, and the gain of the automatic gain control amplifier is controlled such that the output noise control value is within a predetermined reference value range. It is.

According to a second aspect of the present invention, a frequency component having a minimum power value in each frequency component is selected based on the frequency spectrum information, and a signal-to-noise ratio of the frequency component having the minimum power value is determined. After the calculation, the frequency of the sampling clock of the A / D converter is controlled so that the signal-to-noise ratio is maintained at a predetermined value or more to suppress the quantization noise component of the A / D converter. .

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on illustrated embodiments. FIG. 1 is a block diagram showing an embodiment of a frequency analysis device according to the present invention.
The frequency analyzer according to the present invention shown in FIG. 1 includes an AGC amplifier 1 for amplifying an analog signal to a predetermined voltage, a low-pass filter 2 for removing a harmonic component of the analog signal amplified by the AGC amplifier 1, An A / D converter 3 for sampling an analog signal filtered by the low-pass filter 2 and converting it into a digital signal;
(FFT) that performs fast Fourier transform processing on the digital signal supplied by the FFT and outputs predetermined frequency spectrum information
(Fourier Transform) means 6 and a detection control unit 7 which calculates an output noise of the A / D converter 3 based on the frequency spectrum information supplied from the FFT means 6 and compares it with a predetermined reference value to generate a detection signal. An AGC control unit 8 for controlling the gain of the AGC amplifier 1 in accordance with the detection signal supplied by the detection control unit 7, and an AGC control unit 8 having an optimum frequency for the A / D converter 3 in accordance with a clock control signal supplied by the output detection control unit 7. A clock control unit 9 for supplying a sampling clock;

The operation of the frequency analyzer shown in FIG. 1 will be described below. First, when no signal is input to the AGC amplifier 1, the AGC amplifier 1 is set to the maximum gain in accordance with the gain control signal supplied by the AGC control unit 8. Then, when a predetermined analog signal is input to the AGC amplifier 1, the AGC amplifier 1 amplifies the signal with the maximum gain, removes the harmonic component by the low-pass filter 2, and removes the A / D converter
To supply. The A / D converter 3 samples the amplified analog signal with a sampling clock supplied from the clock controller 9, converts the sampled analog signal into a digital signal, and supplies the digital signal to the FFT means 6. The FFT means 6 performs fast Fourier transform processing on the digital signal, outputs frequency components contained in the analog signal as frequency spectrum information, and supplies the frequency component to the detection control unit 7.

The detection control unit 7 performs frequency and power values (or voltage values) of main frequency components S1, S2, S3,... Sn constituting an analog signal (= S) based on the frequency spectrum information. Get. Further, the detection control unit 7 determines the frequency components S1, S2, S3,.
The output noise Naj of the A / D converter 3 is calculated for each frequency component from information on the peripheral frequency of n and the power value (voltage value).
Here, the noise power Na of each frequency component is calculated based on the equation (2).
Naj (S1), Na as a contribution (element) to j
j (S2), Naj (S3),... Naj (S
n) is calculated and the sum of the calculated values is defined as output noise Naj.

Then, the output noise Naj is held as a noise control value and is compared with a preset reference value. here,
When the noise control value is larger than the reference value, the detection control unit 7
A detection signal is output to instruct the AGC control unit 5 to decrease the gain of the AGC amplifier 1, and when the noise control value is smaller than the reference value, A is increased to increase the gain of the AGC amplifier 1.
An instruction is given to the GC control unit 5. Here, since the gain of the AGC amplifier 1 is the maximum and the noise control value is larger than the reference value, the detection control unit 7 outputs a detection signal and decreases the gain of the AGC amplifier 1 by a predetermined amount (for example, 1 dB step). The AGC control unit 8 is instructed to perform the operation.

The AGC control section 8 outputs a gain control signal in accordance with the detection signal to reduce the gain of the AGC amplifier 1 by a predetermined amount (for example, 1 dB step). The AGC control unit 5 amplifies the analog signal again with the newly set gain, and supplies this to the A / D converter 3 via the low-pass filter 2. The A / D converter 3 converts this into a digital signal again, and
It is supplied to the FT means 6. The FFT means 6 processes this further, generates spectrum information again, and supplies it to the detection control unit 7. By repeating the above, the noise control value calculated by the detection control unit 7 also decreases as the gain of the AGC amplifier 1 gradually decreases. When the noise control value falls within the range of the reference value (NREF), the detection control section 7 outputs a detection signal and sets the AG so that the gain of the AGC amplifier 1 is fixed.
Instruct C control unit 8.

Here, the reference value is obtained by previously calculating the quantization noise Nq and the differential non-linear noise Nd generated at the output of the A / D converter according to the equation (1), and referring to this, an appropriate value is obtained. Although the values are set, those actually measured in advance may be used as reference values for setting the reference values. In this manner, the frequency spectrum information of the input analog signal is calculated by the FFT means 6, and the A / D calculated based on this is calculated.
Since the output noise power (voltage) of the converter 3 is held and the gain of the AGC amplifier 1 is controlled so as to be within the range of the reference value, the AGC is controlled so that the output noise of the A / D converter 3 does not increase. The gain of the amplifier 1 is optimized according to the input frequency.

Next, an example of controlling the frequency of the sampling clock of the A / D converter 3 will be described. AG mentioned above
When the gain control of the C amplifier 1 is completed, the sampling clock (maximum frequency) is supplied from the clock control unit 9 to the A / D converter.
It is supplied to the converter 3. The detection controller 7 selects a frequency component (Smin) having the lowest signal level according to the frequency spectrum information obtained from the FFT means 6. Then, the signal-to-noise ratio of Smin (Smin / N)
Is calculated. Here, the noise N is obtained by calculating the noise power of a predetermined band based on the spectrum information obtained by the FFT means 6. In calculating the noise power, the noise power is calculated for the band occupied by the main frequency component. Needless to say, it is excluded from the target area to be performed.

Next, the signal-to-noise ratio of Smin is compared with a reference value (= α). When the signal-to-noise ratio is larger than α, the clock control signal is sent to the clock control unit 9. The clock control unit 9 controls A /
The frequency of the sampling clock supplied to the D converter 3 is reduced from the maximum value. When the frequency of the sampling clock decreases, the quantization noise density output from the A / D converter 3 increases. Then, the signal-to-noise ratio of Smin is calculated again and compared with the reference value. By repeating this, the S
When the signal-to-noise ratio of min falls within the range specified by the reference value, the frequency of the sampling clock is fixed.

When the signal-to-noise ratio of Smin is initially smaller than the reference value (= α), the frequency of the sampling clock remains fixed at the maximum value. As described above, the signal-to-noise ratio of the component having the lowest signal level among the frequency components of the input analog signal has at least the reference value (=
α) is maintained and analysis can be performed with the frequency analyzer.
Since the frequency of the sampling clock of the / D converter 3 is controlled to be as small as possible, the power consumption of the A / D converter 3 can be minimized.

In the embodiment of the present invention described above,
Although the method of controlling the gain of the AGC amplifier 1 and the method of controlling the sampling clock frequency of the A / D converter 3 are combined, it is needless to say that the effect can be improved by any one method.

[0023]

As described above, according to the present invention, in a frequency analyzer for analyzing a frequency component of an analog signal, an input analog signal is amplified by an AGC amplifier and A
A / D converter, which converts the digital signal into a digital signal with the A / D converter, extracts main frequency components by FFT means to obtain frequency spectrum information, and outputs the output of the A / D converter from the frequency spectrum information. Calculating the noise, controlling the gain of the AGC amplifier so that the output noise is at an optimum level, and calculating the signal-to-noise ratio of the minimum level frequency component based on the frequency spectrum information; Is maintained at a predetermined value by reducing the frequency of the sampling clock of the A / D converter as much as possible.
Since the quantization noise power density output from the A / D converter is reduced, a frequency analyzer capable of fully utilizing the dynamic range of the A / D converter and suppressing the noise generated at the output as much as possible. Works well in offering.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a frequency analysis device according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a conventional frequency analyzer.

FIG. 3 is a diagram showing output noise of an A / D converter.

FIG. 4 is a diagram showing quantization noise of an A / D converter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... AGC amplifier 2 ... Low-pass filter 3 ... A / D converter 4 ... Clock oscillator 5, 8 ... AGC control part 6 ... FFT means 7 ... Detection control part 9 Clock control unit

Claims (2)

[Claims] An automatic gain control amplifier for amplifying an analog signal to a predetermined voltage; an A / D converter for sampling a signal of a predetermined voltage supplied by the automatic gain control amplifier and converting the signal to a digital signal; A Fourier transforming means for processing the digital signal output from the converter and outputting the frequency and power of the frequency component included in the analog signal as frequency spectrum information, wherein the input voltage of the A / D converter And controlling the gain of the automatic gain control amplifier so as to suppress the output noise component of the A / D converter generated in proportion to each square of the frequency and the frequency. The frequency component is controlled based on the frequency spectrum information. Calculate the elements contributing to the output noise component of, the output noise control value is the sum of the elements over all frequency components, A frequency analyzer wherein the gain of the automatic gain control amplifier is controlled so that an output noise control value falls within a predetermined reference value range. 2. A frequency component having a minimum power value in each frequency component is selected based on the frequency spectrum information, and a signal-to-noise ratio of the frequency component having the minimum power value is calculated. The frequency of the sampling clock of the A / D converter is controlled so that the A / D
The frequency analysis device according to claim 1, wherein a quantization noise component of the converter is suppressed.