age. Use separate analog and digital PC board ground

sections with only one star point (Figure 14) connecting

the two ground systems (analog and digital). For lowest

noise operation, ensure the ground return to the star

ground’s power supply is low impedance and as short

as possible. Route digital signals far away from sensi-

tive analog and reference inputs.

influence the proper operation of the ADC’s fast com-

two parallel capacitors, 0.1µF and 4.7µF, located as

close as possible to the MAX1236–MAX1239 power-sup-

ply pin. Minimize capacitor lead length for best supply

noise rejection, and add an attenuation resistor (5

Ω) in

series with the power supply if it is extremely noisy.

Definitions

Integral Nonlinearity

Integral nonlinearity (INL) is the deviation of the values on

an actual transfer function from a straight line. This straight

line can be either a best straight-line fit or a line drawn

between the endpoints of the transfer function, once offset

and gain errors have been nullified. The MAX1236–

MAX1239’s INL is measured using the endpoint.

Differential Nonlinearity

Differential nonlinearity (DNL) is the difference between

an actual step width and the ideal value of 1 LSB. A

DNL error specification of less than 1 LSB guarantees

no missing codes and a monotonic transfer function.

Aperture Jitter

the time between the samples.

Aperture Delay

edge of the sampling clock and the instant when an

actual sample is taken.

Signal-to-Noise Ratio

For a waveform perfectly reconstructed from digital sam-

ples, the theoretical maximum SNR is the ratio of the full-

scale analog input (RMS value) to the RMS quantization

error (residual error). The ideal, theoretical minimum ana-

log-to-digital noise is caused by quantization error only

and results directly from the ADC’s resolution (N Bits):

In reality, there are other noise sources besides quanti-

zation noise: thermal noise, reference noise, clock jitter,

etc. SNR is computed by taking the ratio of the RMS

signal to the RMS noise, which includes all spectral

components minus the fundamental, the first five har-

monics, and the DC offset.

Signal-to-Noise Plus Distortion

Signal-to-noise plus distortion (SINAD) is the ratio of the

fundamental input frequency’s RMS amplitude to the

RMS equivalent of all other ADC output signals.

2.7V to 3.6V and 4.5V to 5.5V, Low-Power,

4-/12-Channel, 2-Wire Serial, 12-Bit ADCs

______________________________________________________________________________________

19

011 . . . 111

011 . . . 110

000 . . . 010

000 . . . 001

000 . . . 000

111 . . . 111

111 . . . 110

111 . . . 101

100 . . . 001

100 . . . 000

- FS

0

INPUT VOLTAGE (LSB)

OUTPUT CODE

ZS = 0

+FS - 1 LSB

FS =

2

-FS =

2

≤

MAX1236-MAX1239

1 LSB =

4096

Figure 13. Bipolar Transfer Function

GND

3V OR 5V

SUPPLIES

DGND

3V/5V

GND

*OPTIONAL

4.7

μF

R* = 5

Ω

0.1

μF

DIGITAL

CIRCUITRY

MAX1236–

MAX1239

Figure 14. Power-Supply Grounding Connection