MAX11040 datasheet(11/31 Pages) MAXIM

11 / 31 page

24-Bit, 4-Channel, Simultaneous-Sampling,

Cascadable, Sigma-Delta ADC

______________________________________________________________________________________

Digital Filter

The MAX11040 contains an on-chip digital lowpass fil-

ter that processes the data stream from each modulator

and generates the high-resolution output data. The low-

pass filter frequency response is determined by the

programmable output data rate. At the nominal 16ksps

output data rate, the -3dB bandwidth of the filter is

3.4kHz. The passband flatness is better than ±0.1dB

from 0 to 1.74kHz. The notches are located at 5.75kHz

and 7.195kHz. These frequencies scale linearly with the

output data rate. See Figure 2 and Table 1 for the fre-

quency response at different data rates.

Since the transfer function of a digital filter is repeatable

and predictable, it is possible to correct for frequency-

dependent attenuation in downstream software. See

the

Compensating for the Rolloff of the Digital Filter in a

Typical FFT Analysis section. The transfer function is

defined by the following equation:

where:

Gain is the filter gain.

fAIN is the analog input frequency.

fSAMPLE is the programmed output data rate, nomi-

nally 16kHz.

fXINCLOCK is the clock frequency at XIN, nominally

24.576MHz.

FIR_Gain (fAIN) is the normalized gain of the FIR fil-

ter with the following filter coefficients, as a function

of the analog input frequency fAIN. These coeffi-

cients are applied at the output data rate:

+ 0.021484375

- 0.072265625

- 0.035156250

+ 0.304687500

+ 0.539062500

+ 0.304687500

- 0.035156250

- 0.072265625

+ 0.021484375

Latency

The digital filter determines the latency of the

MAX11040. Latency is defined as the time between the

effective point in time that a sample is taken and when

the resulting digital data is available for reading.

The latency of the converter is specified by the follow-

ing equation:

Latency = (6 x tDOUT) + (PHI x 1.3µs) + 30µs

where tDOUT is the data output period (inverse of the

programmed sample rate), determined by fXINCLOCK

and the selected output data rate, and PHI is the pro-

grammed sampling instant delay for the channel in

question (0

≤ PHI ≤ 255). The latency is approximately

405µs at 16ksps.

Gain f

FIR Gain f

AIN

SAMPLE

AIN

XINCLOCK

AIN

()

sin

)

⎛

⎝⎜

⎞

⎠⎟

⎛

⎝⎜

⎞

⎠⎟

⎛

⎝

⎜

⎜⎜

⎞

⎠

⎟

⎟⎟

()

Table 1. Bandwidth vs. Output Data Rate

OUTPUT DATA

RATE (ksps)

-3dB BANDWIDTH

(kHz)

-0.1dB BANDWIDTH

(kHz)

0.5

0.11

0.05

0.21

0.11

0.42

0.22

0.85

0.43

1.69

0.87

2.11

1.09

2.54

1.31

3.38

1.74

6.78

3.48

13.5

6.96

fAIN/fSAMPLE

0.24

0.20

0.16

0.12

0.8

0.4

-5

-4

-3

-2

-1

-6

0.28

Figure 2. Digital Filter Response

MAX11040 Datasheet(PDF) 11 Page - Maxim Integrated Products

MAX11040 Datasheet(HTML) 11 Page - Maxim Integrated Products

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Datasheet Download

Link URL