IBIS4-1300
Document Number: 38-05707 Rev. *B
Page 19 of 37
Control of the VLOW_ADC & VHIGH_ADC reference voltages
VLOW_ADC & VHIGH_ADC are the reference voltages for a
0 and 1023 code. A 2K-resistor ladder internally connects
them. The appropriate 2 V and 4 V DC voltages can be
obtained as in Table 7. : pins of the ADC, and decoupled to
ground.
Non-linear and linear conversion mode - "gamma" correction
Figure 14. linear and non-linear ADC conversion characteristic
Figure 14. shows the ADC transfer characteristic. For this
measurement, the ADC input was connected to a 16-bit DAC.
The input voltage was a 100 KHz triangle waveform.
The
non-linear
ADC
conversion
is
intended
for
gamma-correction of the images. It increases contrast in dark
areas and reduces contrast in bright areas. The non-linear
VLOW_ADC
71
Low reference and high reference voltages of ADC should be 2V to 4V.
The resistance between VLOW_ADC and VHIGH_ADC is about 1.5 K, thus this
range can be approximated by tying LOW with 2K to GND
And HIGH with 1K to VDD.
VHIGH_ADC
61
PBIASDIG1
64
Connect with 100K to GND and decouple to VDD
PBIASENCLOAD
65
Connect with 100K to GND and decouple to VDD
PBIASDIG2
66
Connect with 100K to GND and decouple to VDD
NBIASANA2
69
Connect with 100K to VDD and decouple to GND
NBIASANA
70
Connect with 100K to VDD and decouple to GND
These resistors determine the analog resp. digital speed /power of the ADC. Both
can be increased/decreased by lowering or increasing the resistance values.
Power & Ground
VDD_DIG
56, 76
Power supply of digital circuits of ADC, + 5 V
VDD_AN
58, 74
Power supply of analog circuits of ADC, + 5 V
GND_DIG
57, 75
Ground of digital ADC circuits
GND_AN
60, 72
Ground of analog ADC circuits
Table 7. pins of the ADC
Name
No.
Description
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
2.0
2.5
3.0
3.5
4.0
Input signal [V]
linear
non-linear
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