time between the falling 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 ADCs res-

olution (N bits):

SNR = (6.02 x N + 1.76)dB

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) indicate the global

accuracy of an ADC at a specific input frequency and

sampling rate. An ideal ADC error consists of quantiza-

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

scale range of the ADC, calculate the effective number

of bits as follows:

ENOB = (SINAD – 1.76) / 6.02

Figure 13 shows the effective number of bits as a func-

tion of the MAX1062’s input frequency.

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.

Supplies, Layout, Grounding

and Bypassing

Use PC boards with separate analog and digital

ground planes. Do not use wire-wrap boards. Connect

the two ground planes together at the MAX1062 (pin 3).

Isolate the digital supply from the analog with a low-

value resistor (10

Ω) or ferrite bead when the analog

and digital supplies come from the same source

(Figure 14).

THD

VVVV

V

=×

+++





















20

1

2

2

3

2

4

2

5

2

log

SINAD dB

Signal

Noise

Distortion

RMS

RMS

(

)

log

=×

+

()

















20

14-Bit, +5V, 200ksps ADC with 10µA Shutdown

______________________________________________________________________________________

15

0.1

10

100

INPUT FREQUENCY (kHz)

1

14

0

2

4

6

8

12

10

Figure 13. Effective Bits vs. Input Frequency

SCLK

DOUT

AGND

DGND

AIN

10

Ω

REF

DOUT

SCLK

CS

AIN

+5V

4.7

µF

0.1

µF

0.1

µF

GND

MAX1062

CS