Layout, Grounding, and Bypassing

For best performance, use printed circuit boards. Do not

run analog and digital lines parallel to each other, and do

not lay out digital signal paths underneath the ADC pack-

age. Use separate analog and digital ground planes with

only one point connecting the two ground systems (ana-

log and digital) as close to the device as possible.

Route digital signals far away from sensitive analog and

reference inputs. If digital lines must cross analog lines,

do so at right angles to minimize coupling digital noise

onto the analog lines. If the analog and digital sections

share the same supply, then isolate the digital and ana-

log supply by connecting them with a low-value (10Ω)

resistor or ferrite bead.

parallel with a 1µF to 10µF low-ESR capacitor and the

smallest capacitor closest to the device. Keep capacitor

leads short to minimize stray inductance.

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 end points of the transfer function,

once offset and gain errors have been nullified. The

static linearity parameters for the MAX1065/MAX1066

are measured using the end-point method.

Differential Nonlinearity

Differential nonlinearity (DNL) is the difference between

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

DNL error specification of 1LSB guarantees no missing

codes and a monotonic transfer function.

Aperture Jitter and Delay

Aperture jitter is the sample-to-sample variation in the

time between samples. Aperture delay is the time

between the rising edge of the sampling clock and the

instant when the actual sample is taken.

Signal-to-Noise Ratio

For a waveform perfectly reconstructed from digital

samples, signal-to-noise ratio (SNR) is the ratio of the

full-scale analog input (RMS value) to the RMS quanti-

zation error (residual error). The ideal, theoretical mini-

mum analog-to-digital noise is caused by quantization

noise error only and results directly from the ADC’s res-

olution (N-bits):

SNR = (6.02 x N + 1.76)dB

where N = 14 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 the other ADC output signals.

Effective Number of Bits

Effective number of bits (ENOB) indicates the global

accuracy of an ADC at a specific input frequency and

sampling rate. An ideal ADC’s error consists of quanti-

zation noise only. With an input range equal to the full-

scale range of the ADC, calculate the effective number

of bits as follows:

Total Harmonic Distortion

Total harmonic distortion (THD) is the ratio of the RMS

sum of the first five harmonics of the input signal to the

fundamental itself. This is expressed as:

Spurious-Free Dynamic Range

Spurious-free dynamic range (SFDR) is the ratio of the

RMS amplitude of the fundamental (maximum signal

component) to the RMS value of the next largest fre-

quency component.

Chip Information

TRANSISTOR COUNT: 15,140

PROCESS: BiCMOS

THD

VVVV

V

=×

+++

⎛

⎝⎜

⎞

⎠⎟

⎡

⎣

⎢

⎢

⎢

⎢

⎢

⎤

⎦

⎥

⎥

⎥

⎥

⎥

20

2

2

3

2

4

2

5

2

1

log

ENOB

SINAD

=

602

.

.

SINAD dB

Signal

Noise Distortion

RMS

RMS

(

)

log

()

=×

+

⎡

⎣

⎢

⎤

⎦

⎥

20

Low-Power, 14-Bit Analog-to-Digital Converters

with Parallel Interface

12

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