HSP50215EVAL 데이터 시트보기 (PDF) - Intersil

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HSP50215EVAL

DSP Modulator Evaluation Board

Intersil 

HSP50215EVAL

the amount of time you care to wait to load the file. A rule of

thumb is to use as large a number as possible. Note that the

start of the noise sequence is determined by when the

stimulus file for that channel is loaded. If multiple channels

are required to be started together, then the board should be

set to use the internal synchronization logic to respond to a

single external SYNCIN command. In noise applications, a

random start on the various channels is often the desired

condition. The purpose of this example is to demonstrate

both using noise stimulus for filter shape evaluation and for

establishing signal plus noise configurations.

Go to the main menu. Select Item (1) and set the following

parameters:

(8)511

(9)48

(0)Returns to main menu

Select Item (2) and set the following parameters:

(8)511

(9)48

(0)Returns to main menu

Select Item (3) and set the following parameters:

(8)511

(9)48

(0)Returns to main menu

Select Item (4) and set the following parameters:

(1)500,000Hz

(2)501,000Hz

(3)QASK

(4)Filters/bypass

(8)16384

(9)3

(0)Returns to main menu

Select main menu (7) to compute the register values.

Select main menu (8) to configure the board.

Select submenu item (5) to configure all channels.

Select submenu item (3) to load both the modulator and

Pattern RAM.

When the submenu reappears, the download is complete.

The output is a Gaussian Noise signal, sampled at 351kHz

and modulated to 500kHz IF. On a spectrum analyzer the

outline of the shaping filter is depicted. On the scope, a noisy

signal that is 0.4Vpp is displayed.

Now lets add back in a modulated signal.

Go to the main menu. Select Item (1) and set the following

parameters:

(9)3

(0)Returns to main menu

Select main menu (7) to compute the register values.

Select main menu (8) to configure the board.

Select submenu item (1) to configure channel 1.

Select submenu item (1) to load the modulator.

When the submenu reappears, the download is complete.

The output is AWGN summed with modulated signal.

The final step is to determine how to set a particular Signal

to Noise Ratio (SNR). In order to determine a C/N or Eb/No

the following system information must be known:

1)The vector length of the I/Q data vector. (This is the

magnitude of the input vector).

2)The standard deviation of the I and Q components of the

noise pattern vector.

3)The DC gains of the data and noise filters.

4)The input sample rates for the data and noise modulators

(it is assumed that the noise sample rate is higher than the

data sample rate).

5) The noise bandwidth of the noise filters.

6) The multiplier settings for the gain in the modulators.

Items 1 through 5 are listed in the headers of the file or in the

control software menus. Item 6 can be obtained from the

computed register values found in the .1, .2, .3 and .4 files.

Background on Eb/No and SNR Calculations

The signal to noise ratio (C/N) is equal to:

C/NdB = 10LOG(A2/2σ2)

where σ is the standard deviation of the I and Q noise

vectors (they are equal), and A is the average length of the

I/Q vector.

The length of the I/Q vector in the stimulus file is modified by

the gain of the shaping filter and the gain of the

programmable attenuator in the HSP50215. The standard

deviation of the noise vector is likewise modified by the gains

of the filter and the attenuator.

After obtaining C/N, conversion to Eb/No is done by

normalizing for the data rate, NBW of the noise filter, and the

modulation type as follows:

Eb/No=C/N-ModFactor-10LOG(symbol rate)+10LOG(NBW).

where NBW is the double sided noise bandwidth of the noise

filter.

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