VXI Technology, Inc.

CHnI+

CHn+

CHn–

CHnI

EXT TRIG

 

1x, 2x, 5x, 10x

FILTER

+

 

MEMORY

DATA &

VMEINTERFACE

DATA

BACKPLANE

 

gain0

16

CONTROLS

÷ 1

+

 

ADC

 

 

μP

 

ADDRESS

 

÷ 10

LPF

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

gain1

 

 

 

 

 

 

 

 

attn

 

 

 

CHANNEL 0

CONTROLS

 

 

VME

 

 

 

TRIG

 

 

 

 

 

DAC

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CONTROL&

 

 

 

 

 

 

FORCE

 

CHANNEL 1 TRIG

 

 

 

 

 

 

 

 

 

 

 

 

 

TRIG

 

POL

 

CHANNEL 2 TRIG

DATA

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHANNEL 3 TRIG

 

 

 

 

GLUE LOGIC

 

 

 

 

 

 

 

 

 

+

EXT TRIG

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DAC

 

 

 

 

 

 

 

 

FIGURE 1-1: SVM2608 BLOCK DIAGRAM

The acquisition process is controlled by two FPGAs that allow for greater flexibility along with higher speed and precision during the digitizing process. As the data is digitized, it is placed in memory. It is then available to the user through the VME interface. Each channel has its own channel memory that can store up to one million samples of data. This data is also made available to the microprocessor for data processing. The samples are stored as words (16 bits). The first sample of a channel is located at the channel’s base address at Offset 0 (0x000000 for Channel 0, 0x200000 for Channel 1, 0x400000 for Channel 2 and 0x600000 for Channel 3). The next sample is located at Offset 2 (0x000002 for Channel 0, etc.) and the third sample is located at Offset 4, etc.

In order to provide better resolution for the measurement, the input signal is amplified accordingly to generate a ±10 VP-Psignal at the input of the ADC. Thus, on different scales, the weight of a bit of digitized data will be different:

SCALE (V)

Bit Weight (μV/count)

1

30.518

2

61.035

5

152.588

10

305.176

20

610.352

50

1525.879

The following equation is used to determine the bit weight at a specified scale:

Bit Weight = Full Scale / 32,768

For example, the Bit Weight of the 10 V range is:

10.0volts / 32768 = 0.0003051757813 V/count

305.176 µV/count

12

SVM2608 Introduction

Page 12
Image 12
VXI SVM2608 user manual Scale