JPH0635184Y2 - FFT analyzer - Google Patents

Description

[Detailed Description of Device] a. [Purpose of Invention] [Industrial Application Field] The present invention relates to simplification of hardware of an FFT analyzer.

[Conventional technology]

FIG. 4 is a configuration block diagram showing a conventional FFT analyzer having a zooming function. The analog input signal Vi applied to the input terminal 10 is converted into a digital signal by the AD converter 1, and the multipliers 31 and 32 convert the local oscillator 4 to each other.
Outputs that differ by 90 ° are mixed and passed through digital filters 51 and 52, respectively, and FPP (Floating Pos.
int Processor: FFT (Fast) with 6
Fourier Transform: fast Fourier transform)
The zoomed frequency spectrum is displayed on the display 8.

[Problems to be solved by the invention]

However, an FFT analyzer with a zooming function requires dedicated hardware for zooming.
For example, as shown in FIG. 4, even when the input is one channel, two digital filters are required for zooming. Generally, a digital filter is expensive, and this is a big problem when manufacturing an FFT analyzer at a low price.

The present invention has been made to solve the above problems,
Reduced the number of digital filters used to lower prices
The purpose is to realize an FFT analyzer.

B. [Constitution of Device] [Means for Solving Problems] The FFT analyzer according to the present proposal stores an AD converter for converting an input signal into a digital signal and a digital signal output from the AD converter. 1 memory means, an oscillator for outputting first and second signals having phases different from each other by 90 °, a multiplication operation of the output of the AD converter and a first signal obtained from the oscillator, or the first memory Through a digital filter that inputs the operation result from this multiplier and outputs a necessary frequency component of the multiplication result. It is characterized in that it is provided with an operation means for performing a fast Fourier operation by directly or holding a signal directly or by the fast Fourier conversion means and displaying the output from this operation means.

[Action]

By performing the frequency shift for zooming in time division using the memory means, one digital filter can be used in time division for one input channel.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of one channel of an FFT analyzer according to the present invention. 10 is an input terminal to which the analog input signal Vi is applied, 1 is an AD converter for converting the input signal Vi into a digital signal, and 11 is this AD converter 1
Output buffer to control the output of, 12 is this output buffer
11 is a bus connected to, 2 is a first memory to which the I / O port is connected to this bus 12, 3 is a multiplier to which the bus 12 is connected to one input, and 4 is a phase difference of 90 ° from each other. A local oscillator (LO) for frequency shifting, which outputs a signal and whose output is the other input of the multiplier 3, 5 is a digital filter for inputting the output of the multiplier 3 to remove unnecessary frequency components, 6 inputs the output of the digital filter 5
FPP for performing FFT calculation and the like, 61 is a second memory incorporated in this FPP6, and 8 is a display for displaying the zoomed frequency spectrum output of the FPP6.

The operation of the apparatus having the above configuration will be described with reference to FIG.

First, the operation is performed as shown in FIG. In this first mode, the output of the buffer 11 is enabled and the output of the oscillator 4 becomes cosω ₀ t. As a result, the output waveform (t) of the AD converter 1 is written in the memory 2 via the buffer 11 and the bus 12, and simultaneously becomes one input of the multiplier 3 and is multiplied by cosω ₀ t. The waveform obtained by passing the signal of the product of the both through the digital filter 5 is the FFT calculation means 6 of the FPP 6.
FFT operation is performed by 2 and written in the memory 61. At this time, the data written in the memory 61 is F (ω) = ▲ ∫ ^∞ _-∞ ▼ (t) exp (-jωt) dt with the transfer function of the digital filter as H (ω).
Letting (1) be, (1/2) H (ω) {F (ω−ω ₀ ) + F (ω + ω ₀ )}
… (2)

In the second mode shown in FIG. 2B, the output of the buffer 11 is disabled and the output of the oscillator 4 is sinω ₀ t. In this state, the contents of the memory 2 are read out via the bus 12 and become one input of the multiplier 3, multiplied by sin ω ₀ t, and the waveform passed through the digital filter 5 is FFT calculated by the FFT calculation means 62 of the FPP 6. Is calculated. At this time, the FFT calculation means 62
The data output from is (1 / 2j) H (ω) {F (ω−ω ₀ ) + F (ω + ω ₀ )}
… (3) FFT calculation means 62 by calculation means 63 in FPP6
By multiplying the data of the formula (3) from j by j and adding the data of the formula (2) from the memory 61, a zooming spectrum H (ω) {F (ω-ω ₀ ) which is a zoomed frequency spectrum is obtained. } (4) is obtained. This zooming spectrum is displayed on the display 8. Actually, in the second mode, the output of the FFT calculating means 62 can be temporarily stored in another area of the memory 61 in the FFP 6, and the contents can be used as the input data of the calculating means 63.

According to the FFT analyzer having such a configuration, the memory is inserted after the AD converter, and the frequency shift is performed in time division when performing zooming, so that the digital filter can be used in time division, which is expensive. The number of digital filters can be halved. Also, the number of multipliers is halved.

FIG. 3 is an explanatory view showing the operation of another embodiment of the FFT analyzer according to the present invention. The configuration is the same as in Fig. 1,
The operation is different in that the output of the digital filter 5 is directly stored in the memory 61 and then the complex FFT operation is performed. That is, as shown in FIGS. 3A and 3B, in the first and second modes, unlike the case of FIGS. 2A and 2B, the digital filter 5 is used.
Is directly stored in the memory 61. Next, FIG. 3 (C)
In the third mode, the contents of the memory 61 are subjected to complex FFT operation by the complex FFT operation means 64 in the FFP 6, and the zooming spectrum output is displayed on the display 8, as shown in FIG.

C. [Effect of Device] As is apparent from the above description, according to the present invention, the number of digital filters used is reduced to reduce the cost.
A T analyzer can be realized with a simple configuration.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the FFT analyzer according to the present invention, FIG. 2 is an explanatory diagram showing the operation of the apparatus shown in FIG. 1, and FIG. 3 is another embodiment of the FFT analyzer according to the present invention. FIG. 4 is a block diagram showing the configuration of a conventional example of an FFT analyzer. 1 ... AD converter, 2 ... first memory means, 3 ... multiplication means, 4 ... oscillation means, 5 ... digital filter means,
61 …… Second memory means, Vi …… input signal.

Claims (1)

[Scope of utility model registration request] 1. An AD converter for converting an input signal into a digital signal, a first memory means for storing a digital signal output from the AD converter, and first and second phases differing in phase from each other by 90 °. A multiplication operation of an oscillator outputting a signal and an output of the AD converter and a first signal obtained from the oscillator or a multiplication operation of the output of the first memory and a second signal obtained from the oscillator A multiplier and a calculation result from this multiplier are input, and a signal that has passed through a digital filter that outputs a necessary frequency component of the multiplication result is converted directly or by a fast Fourier transform means and temporarily held. An FFT analyzer that is equipped with a calculation means for performing fast Fourier calculation in and displays the output from this calculation means.