SBAS883A February 2018 – June 2018 OPT3101
PRODUCTION DATA.
The ambient cancellation circuit provides the dc and low-frequency diode current while biasing the diode at 1 V. Figure 22 shows the frequency response of the ambient cancellation circuit. A diode current with frequency below fc2 has second-order rejection. The corner frequency fc2 is designed to be at 50 kHz for IAMB_MAX_SEL = 0 (20 µA ambient current support). Below frequency fc1 (approximately at 10 Hz), attenuation becomes first-order. So for a frequency of 1 kHz, the rejection would be (50 kHz / 1 kHz) × 2 = 2500 = 68 dB.
The maximum ambient current supported is programmable from 10 μA to 200 µA, listed in Table 5. Noise contribution from the ambient cancellation block increases with increase in ambient current support, shown in Figure 2. For low-ambient systems, the lower value of maximum ambient support should be used to reduce the noise contribution from the ambient cancellation. Ambient current is also converted to digital using an ADC (AMB_DATA) at the output of the ambient cancellation block. Ambient ADC resolution is 0.104 µA/LSB with 20-µA support. Ambient ADC resolution scales linearly with maximum ambient current supported. Ambient current can be calculated from the AMB_DATA using Equation 7.
where
PARAMETER | ADDRESS | DESCRIPTION |
---|---|---|
IAMB_MAX_SEL | 72h[7:4] | Selects the value of maximum ambient current support
0: 20 µA | 5: 10 µA | 10: 33 µA | 11: 50 µA | 12: 100 µA | 14: 200 μA | Other values: Not valid |