MAX1062_09 Datasheet, PDF (15/18 Pages) Maxim Integrated Products – 14-Bit, +5V, 200ksps ADC with 10μA Shutdown

14-Bit, +5V, 200ksps ADC with 10µA Shutdown
14
12
10
8
6
4
2
f_SAMPLE = 200kHz
0
0.1
1
10
100
INPUT FREQUENCY (kHz)
Figure 13. Effective Bits vs. Input Frequency
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.
( ) ^⎡
SINAD(dB) = 20 × log ^⎢
Signal_RMS
⎤
⎥
⎣⎢ ^{Noise + Distortion} RMS ⎦⎥
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:
⎡
THD = 20 × log^⎢⎢
⎣⎢
V₂ ²
+
V₃ ²
+
V₄ ²
+
V₅ ²
⎤
⎥
V1
⎥
⎦⎥
where V₁ is the fundamental amplitude and V₂ through
V₅ are the 2nd- through 5th-order harmonics.
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 (10Ω) or ferrite bead when the analog
and digital supplies come from the same source
(Figure 14).
AIN
V_REF
4.7µF
+5V
AIN
CS
SCLK
REF
DOUT
AV_DD ^MAX1062
10Ω
0.1µF
DV_DD
0.1µF
AGND
DGND
CS
SCLK
DOUT
GND
Figure 14. Powering AV_DD and DV_DD from a Single Supply
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