FS970X

Rev. 4.4

28/46

Reading and operation of ADC

As described in 8.2, the circuitry of FS970X ADC might drift and causes an offset voltage because of

manufacturing process. This might cause variance to the reading of ADC. To eliminate the offset variance, it’s

necessary to change the setup CYS<1:0> of register SETADC. There are three different working modes.

These modes influence the reading and operation of high-resolution and low-resolution. They are described as

below:

11..1

High-resolution, low-speed output

When CYS<1:0>=00, the input of ADC becomes short; then, we can read the negative value of offset voltage of

ADC from SUM1.

When CYS<1:0>=11, the equivalent digit value of the voltage can be read from SUM1, as shown in Formula 5.

When CYS<1:0>=01, then, the reading value of SUM1 is equal to the ideal reading of linear ADC of the voltage.

Its transfer function is shown as Formula 3. It can be used for all the measurement for high resolution.

When CYS<1:0>01, the output frequency of SUM1is the first zero-point frequency

1

Z

f

of COMB1, as shown

in Formula 9. When CYS<1:0> =01, the output frequency equals

2

1

Z

f

.

11..2

Low-resolution, high-speed output

When CYS<1:0>=00, the input of ADC becomes short; then, we can read the negative value of offset voltage of

ADC from SUM2. It can be used

os

D

self-calibration.

When CYS<1:0>=11, the equivalent digit value of the voltage can be read from SUM2, as shown in Formula 5.

It can be used for peak-hold sampling measurement.

When CYS<1:0>=01, the transfer function of low resolution output SUM2 should become (a revision from

Formula 5)

Formula 9...........................

























































0

2

0

2

2

'

'

SUM

V

v

G

D

SUM

D

V

v

G

SUM

ref

x

os

os

ref

x

The value of

os

D

can be read from SUM2 when power-on or turning the rotary, set CYS<1:0>=00. Therefore,

the flow-Chart of operation and display of fast ADC output is shown as Graph 13. Whereas,

x

D

is the ideal

ADC values of non-offset voltage, calculated from SUM2. It can be used for Bargraph display of all kinds of high

resolution measurement.