7.1 Noise Performance
Adjust the oversampling ratio (OSR) to control the data rate and change the digital filter in order to optimize the noise performance of the ADS127L01. Hardware control pins offer four oversampling options and three selectable digital filter options to configure the ADC for a specific bandwidth of interest. When averaging is increased by reducing the data rate (increasing the OSR), the in-band noise drops as more samples from the modulator are averaged to yield one conversion result. Table 1 and Table 2 summarize the device noise performance across the various oversampling and digital filter options. Wideband 1 filter has a filter transition band of (0.45 to 0.55) fDATA, and Wideband 2 filter has a filter transition band of (0.40 to 0.50) fDATA. Data are representative of typical noise performance at TA = 25°C with an external 2.5-V reference. Data shown are the result of one standard deviation of the readings with the inputs shorted together and biased to midsupply. A minimum of 1,000 consecutive readings are used to calculate the VRMS_noise voltage noise for each measurement. Equation 1 is used to convert the noise in VRMS_noise to SNR, and Equation 2 is used to convert the noise in VRMS_noise to ENOB. The peak-to-peak noise for the Low-latency filter is defined as VPP_noise.
Equation 1. SNR = 20 × log (VREF × 0.7071 / VRMS_noise)
Equation 2. ENOB = In (2 x VREF / VRMS_noise) / In (2)
Table 1. Wideband Filters Performance Summary
at AVDD = 3.0 V, DVDD = 1.8 V, and 2.5-V Reference
MODE |
DATA RATE (SPS) |
OSR |
TRANSITION BAND |
PASS BAND (kHz) |
SNR (dB) |
VRMS_noise (μVRMS) |
ENOB |
IDVDD
(mA) |
High-resolution (HR) |
512,000 |
32 |
Wideband 1 filter |
230.4 |
103.7 |
11.61 |
18.72 |
7.50 |
Wideband 2 filter |
204.8 |
104.1 |
10.64 |
18.84 |
256,000 |
64 |
Wideband 1 filter |
115.2 |
107.3 |
7.61 |
19.33 |
4.35 |
Wideband 2 filter |
102.4 |
107.7 |
7.25 |
19.40 |
128,000 |
128 |
Wideband 1 filter |
57.6 |
110.4 |
5.35 |
19.83 |
2.80 |
Wideband 2 filter |
51.2 |
110.9 |
5.06 |
19.91 |
64,000 |
256 |
Wideband 1 filter |
28.8 |
113.4 |
3.79 |
20.33 |
2.00 |
Wideband 2 filter |
25.6 |
113.9 |
3.58 |
20.41 |
Low-power (LP) |
256,000 |
32 |
Wideband 1 filter |
115.2 |
103.9 |
11.27 |
18.76 |
3.80 |
Wideband 2 filter |
102.4 |
104.7 |
10.31 |
18.89 |
128,000 |
64 |
Wideband 1 filter |
57.6 |
107.6 |
7.38 |
19.37 |
2.25 |
Wideband 2 filter |
51.2 |
108.1 |
6.96 |
19.45 |
64,000 |
128 |
Wideband 1 filter |
28.8 |
110.7 |
5.18 |
19.88 |
1.50 |
Wideband 2 filter |
25.6 |
111.1 |
4.95 |
19.95 |
32,000 |
256 |
Wideband 1 filter |
14.4 |
113.7 |
3.67 |
20.38 |
1.10 |
Wideband 2 filter |
12.8 |
114.1 |
3.47 |
20.46 |
Very-low-power (VLP) |
128,000 |
32 |
Wideband 1 filter |
57.6 |
104.1 |
11.01 |
18.79 |
1.95 |
Wideband 2 filter |
51.2 |
104.9 |
10.11 |
18.92 |
64,000 |
64 |
Wideband 1 filter |
28.8 |
107.8 |
7.20 |
19.41 |
1.20 |
Wideband 2 filter |
25.6 |
108.3 |
6.80 |
19.49 |
32,000 |
128 |
Wideband 1 filter |
14.4 |
110.9 |
5.07 |
19.91 |
0.80 |
Wideband 2 filter |
12.8 |
111.3 |
4.81 |
19.99 |
16,000 |
256 |
Wideband 1 filter |
7.2 |
113.9 |
3.59 |
20.41 |
0.60 |
Wideband 2 filter |
6.9 |
114.3 |
3.41 |
20.48 |
Table 2. Low-Latency Filter Performance Summary
at AVDD = 3.0 V, DVDD = 1.8 V, and 2.5-V Reference
MODE |
DATA RATE (SPS) |
OSR |
-3-dB BANDWIDTH (kHz) |
SNR (dB) |
VRMS_noise (μVRMS) |
ENOB |
VPP_noise (μVPP) |
IDVDD
(mA) |
High-resolution (HR) |
512,000 |
32 |
101.8 |
107.6 |
7.40 |
19.37 |
64.67 |
1.60 |
128,000 |
128 |
50.6 |
110.8 |
5.12 |
19.90 |
44.11 |
1.39 |
32,000 |
512 |
13.7 |
116.2 |
2.74 |
20.80 |
24.14 |
1.33 |
8,000 |
2048 |
3.5 |
122.0 |
1.41 |
21.76 |
11.32 |
1.32 |
Low-power (LP) |
256,000 |
32 |
50.9 |
107.8 |
7.22 |
19.40 |
61.99 |
0.85 |
64,000 |
128 |
25.3 |
111.0 |
4.97 |
19.94 |
46.79 |
0.75 |
16,000 |
512 |
6.9 |
116.5 |
2.65 |
20.85 |
22.05 |
0.73 |
4,000 |
2048 |
1.7 |
122.2 |
1.37 |
21.80 |
10.73 |
0.72 |
Very-low-power (VLP) |
128,000 |
32 |
25.5 |
108.1 |
6.97 |
19.45 |
65.57 |
0.50 |
32,000 |
128 |
12.7 |
111.3 |
4.80 |
19.99 |
39.64 |
0.44 |
8,000 |
512 |
3.4 |
116.7 |
2.57 |
20.89 |
20.27 |
0.41 |
2,000 |
2048 |
0.9 |
122.4 |
1.34 |
21.83 |
10.73 |
0.40 |