FS9701B datasheet(31/46 Pages) FORTUNE

31 / 46 page

FS970X

Rev. 4.4

31/46

Formula 11

5000002384

......

(

)

0001

0000

(

1111

































SUM

As shown in Formula 3, when the gain

equals the ideal value 1, the reference voltage

ref

equals

1.00000V. From the reading of ADC 0010_1000_0000_0000_0000_000, the voltage can be calculated as:

62500

625

00000











ref

When the reading of ADC is 1101_1111_1111_1111_1111_1111, the voltage can be calculated as:

50000

5000002384

00000















ref

However, in reality, the

value affected by the drifting of the process, will not equal to 1.It will vary approx.



. At the same time, the reference voltage

ref

, affected by the reference power and dividing resistance,

will not equal to 1.00000V. Therefore, the gain variances from the components have to be calibrated.

The different output code of different models

FS970X chip series has three models with different resolution, 5,000 digits, 20,000 digits, and 50,000 digits.

The digit output codes are as follows:

In the 5,000 digits or 50,000 digits models, when the absolute value of SUM1, and the SUM1<21:18> is greater

than 1010, then, the SUM1<21:18>will saturate to 1111. And the equivalent voltage of SUM1<21:18>=1010 will

be approx. 0.625V.

In the 20,000 model, when the absolute value of SUM1, and the SUM1<21:18> is greater than 0101, then, the

SUM1<21:18>will saturate to 1111. And the equivalent voltage of SUM1<21:18>=1010 will be approx. 0.3125V.

In the 5,000 digit model, the digital output of SUM1<5:1> is a constant 00000.

Other Control setting

ENAD(ADG<7>) is the enabling signal of ADC. It turns on the ADC when value =1, and turns

off the ADC when value=0. It saves the power consumption setting the value to 0.

12. Digital Signal Process

Except digital filter, the digital signal process of FS970X includes frequency counter and peak-hold sampling

process.

Frequency counter

The frequency counter of FS970X is composed of time-based counter and signal counter. The physical value

of the target can be calculated from these two counters. The physical values of the target have signal frequency

and duty cycle. It is determined by the DTON. It performs the frequency counter when setting it as “Lo” and

performs duty cycle measurement when setting to as “Hi”.

When performing the frequency counter measurement, it needs the reference time pulse signal FTB, as shown

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