CN1178616A - Process for monitoring quantisation quality in digital data - Google Patents

Abstract

In order to monitor the transmission quality of digitized signals, the quantization interference power is measured in a region where no useful signal is being transmitted. The quantization step for an associated D/A converter can be determined from the quantization interference power, and an assessment can be made, based on a comparison, as to whether the D/A converter is meeting the required quality parameters.

Description

The method of monitoring quantisation quality in digital data

What invention related to is the method for monitoring quantisation quality in digital data, and digitized signal is by quantization.

Prior art

For signal noise ratio, for example measurement of digital to television picture intelligence noise ratio can be considered with check signal, for example the test lattice in the TV image.But this mode is to be prerequisite with consuming time and expensive verification receiver and corresponding measuring technique.The monitoring of control signal needs similar expense.

The advantage of invention

According to the feature of major requirement, in transmission course, can estimate digitized signal in simple mode with the measure of invention is its transmission quality, and does not need interruption of work.Simply mode is estimated the D/A parallel operation operate as normal whether in the communication line.

Invention is based on following knowledge:

The resolution of D/A converter and mass parameter thereof is held in direct ratio in the transmission quality of obtainable digitized signal (for example signal noise ratio) and the communication line.The starting point of invention is, change under the situation about enough controlling (for sinusoidal carrier or multichannel signal at A/D, usually＞6Bit, as occurring in the TV), when analog signal equably during quantization, the final amount of throughput sub level produces the mistake that has white gaussian-shape noise properties.This white noise promptly is assigned in those frequency ranges of not transmitting useful signal by the uniform distribution of Nyquist wave spectrum.By the measurement of quantization interference power, the especially measurement of its mean value can be determined quantization level a for D/A converter in these frequency ranges, and itself and desired value are compared.If unacceptable big deviation between quantization level a that records and desired value, occurred, handle rub-out signal so, rub-out signal is for example announced at the center by remote control.

Like this, with regard to transmission quality, many D/A converters in the TV distribution network for example in the time of can monitoring simultaneously, also can obtain experience by the long-time stability of D/A converter.

Accompanying drawing

Further specify inventive embodiment by accompanying drawing.Fig. 1 has shown the block diagram of D/A converter quality testing, and Fig. 2 is the radio broadcasting in the wideband network and the position of television channel.

Describe

In the distribution network of radio broadcasting and TV signal, broadcasting and TV signal for example select the system signal form by glass fibre GF transmission with the digitlization multichannel, change it into simulation multichannel again at user TLN place by means of quick D/A converter and select the system signal, this signal can further be handled by commercialization broadcasting and/or television receiver.In Fig. 2, introduced the example of this multichannel selection system signal.

Because the signal noise ratio of digitlization, quantization transmission signals directly is directly proportional with the resolution of D/A converter, quality testing can be limited on this parameter.Such as already mentioned, its starting point is, when the A/D conversion (ADC1 among Fig. 1) of transmitting terminal, carry out enough control (for sinusoidal carrier or multichannel signal, usually＞6Bit), when analog signal equably during quantization, the final amount by digital translation level a produces the mistake that has white gaussian-shape noise properties.Usually, for average quantization interference power or quantization power noise (W.K aiser professor's lecture teaching materials, transmission technology II, Universitaet Stuttgart, nineteen eighty-two, 229-230 page or leaf) arranged: $P_q=\frac{a^2}{12}$ A is the quantization level.

The noise that causes thus (certainly and other noise sources such as thermal noise superimposed) uniform distribution on the Nyquist wave spectrum does not distribute on those do not transmit the position of useful signal yet.By measuring average quantization interference power, it is greater than other noise component certainly, can determine quantization level a.

The frequency (perhaps 5.5MHz or 450KHz) of 10.7MHz can be provided on a position that is not taken by useful wave spectrum.Because can obtain corresponding filter, so on these frequency locations, can easily arrange an amplifier sensitivity, high selectivity.Following numerical value is applicable to the television distribution system of realization.For resolution is 12Bit, and outlet voltage was the D/A converter quantization level of 1V ss when resistance was 50 ohm $a=\frac{1\mathrm{<figure-callout\; id="2"\; label="Vss"\; filenames="A9619249000071.png"\; state="\{\{state\}\}">Vss</figure-callout>}}{2^{12}}=244\mathrm{\&mu;V}$ Correspondingly, average quantization interference power $P_q=\frac{a^2}{12}=4.{9_e}^{-9}W=-76\mathrm{dBm}$

This interference power is distributed on the whole Nyquist frequency bandwidth, and therefore, half scanning frequency is $\frac{452\mathrm{<figure-callout\; id="2"\; label="MHz"\; filenames="A9619249000071.png"\; state="\{\{state\}\}">MHz</figure-callout>}}{2}=226\mathrm{MHz}$

Owing to only measure 10.7MHz in the bandwidth of 300kHz, the frequency of 5.5MHz or 450kHz is so be modified to the interference power of expectation $10\log \frac{300\mathrm{kHz}}{226\mathrm{MHz}}=-28.7\mathrm{dBm}$ The interference power of expecting on the 300kHz bandwidth adds up to

P _q300＝-76dBm-28.7dBm＝-104.7dBm

In the distribution system of realizing, should identify 8Bit and go up degenerating of D/A converter, the expectation interference power of a 8BitD/A transducer adds up to-104.7dBm+4.dBm=-80.7dbm (annotation of translation: numerical computations is wrong)By preselected VS, the outlet signal of DAC arrives amplifier V1 earlier, arrives the first ceramic filter KF1 then.Occur in amplifier stage V2 and V3 that level raises and mate with the second ceramic filter KF2.After amplifying V4, level waits processing for the noise signal of+4dBm on rectifier and integrating circuit GF.A/D converter ADC2 has calculated interference voltage, and upward sends it to data processing A in corresponding crosspoint by system's control.

Under the simplest situation, comparison circuit is suitable for data processing, and this comparison circuit compares measured signal and the desired value that records on D/A converter.If this difference 〉=4 in an embodiment, promptly the desired value of resolution a=12 is lower than more than 4 or 4, so, rub-out signal is handled and is announced.

The solution of suggestion can the monitoring of simple ground in the signal noise ratio of D/A converter.By substituting the further cost saving of single amplifier, also can change measuring frequency by replacing ceramic filter with commercial ZF amplifier.If the prefilter with continuously-tuning among oscillator and mixer stage replacement Fig. 1 can detect spectral range arbitrarily so.

Claims (4)

1. monitoring is realized with following measure by quantized digitized signal method for quality:

-do not transmit one and to measure the quantization interference power in the scope of useful signal,

-from the quantization interference power, determine the quantization level of affiliated D/A converter, and itself and a desired value are compared,

-when the quantization level that records is compared the deviation that has surpassed predetermined permission with desired value, handle rub-out signal so.

2. according to the method for claim 1, it is characterized in that transmission for digital radio broadcasting and/or TV signal, the quantization level that records and deviation from the desired value are 4 or greater than 4 o'clock, will be as the announcement of dislocation signal.

3. according to the method for claim 1 or 2, it is characterized in that selecting the system signal, in a TV signal distribution network, carry out the measurement of quantization interference power for the multichannel at 10.7MHz place.

4. according to the method for claim 3, it is characterized in that selecting the measurement frequency bandwidth of 300kHz.

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