MAX11040(2009) 데이터 시트보기 (PDF) - Maxim Integrated

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MAX11040
(Rev.:2009)

24-Bit, 4-Channel, Simultaneous-Sampling, Cascadable, Sigma-Delta ADC

Maxim Integrated 

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.

1

0

-1

-2

-3

-4

-5

-6

0

0.4 0.8 0.12 0.16 0.20 0.24 0.28

fAIN/fSAMPLE

Figure 2. Digital Filter Response

Table 1. Bandwidth vs. Output Data Rate

OUTPUT DATA

RATE (ksps)

0.5

1

2

4

8

10

12

16

32

64

-3dB BANDWIDTH

(kHz)

0.11

0.21

0.42

0.85

1.69

2.11

2.54

3.38

6.78

13.5

-0.1dB BANDWIDTH

(kHz)

0.05

0.11

0.22

0.43

0.87

1.09

1.31

1.74

3.48

6.96

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:

( ) Gain(fAIN

)

=

⎛

⎜

⎜

⎜

⎝⎜⎜

⎛

sin⎝⎜

π

×

fAIN

fSAMPLE

⎞

⎠⎟

⎛

sin⎝⎜

π

×

fAIN

fXINCLOCK

⎞

⎠⎟

⎞

⎟

⎟

⎟

⎠⎟⎟

3

FIR _ Gain(fAIN )

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.

______________________________________________________________________________________ 11

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