MAX1284-MAX1285 Datasheet, PDF (14/15 Pages) Maxim Integrated Products – 400ksps/300ksps, Single-Supply, Low-Power, Serial 12-Bit ADCs with Internal Reference

400ksps/300ksps, Single-Supply, Low-Power,
Serial 12-Bit ADCs with Internal Reference
SUPPLIES
VDD
VDD GND
R* = 10Ω
4.7µF
0.1µF
VDD
GND
MAX1284
MAX1285
VDD DGND
DIGITAL
CIRCUITRY
*OPTIONAL
Figure 14. Power-Supply Grounding Condition
Aperture Jitter
Aperture jitter (t_AJ) is the sample-to-sample variation in
the time between the samples.
Aperture Delay
Aperture delay (t_AD) is the time defined between the
falling edge of CS and the instant when an actual sample
is taken.
Signal-to-Noise Ratio
For a waveform perfectly reconstructed from digital sam-
ples, signal-to-noise ratio (SNR) is the ratio of full-scale
analog input (RMS value) to the RMS quantization error
(residual error). The theoretical minimum analog-to-digital
noise is caused by quantization error, and results directly
from the ADC’s resolution (N bits):
SNR = (6.02 x N + 1.76)dB
In reality, there are other noise sources besides quantiza-
tion noise, including thermal noise, reference noise, clock
jitter, etc. Therefore, 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
harmonics, 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 RMS
equivalent of all other ADC output signals.
SINAD (dB) = 20 x log (Signal_RMS/Noise_RMS)
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 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
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
x
log


V₂₂
+
V₃₂
+
V₄₂
+
V₅₂


V₁

where V₁ is the fundamental amplitude, and V₂ through
V₅ are the amplitudes of the 2nd through 5th-order har-
monics.
Spurious-Free Dynamic Range
Spurious-free dynamic range (SFDR) is the ratio of RMS
amplitude of the fundamental (maximum signal compo-
nent) to the RMS value of the next largest distortion
component.
___________________Chip Information
TRANSISTOR COUNT: 4286
PROCESS: BiCMOS
14 ______________________________________________________________________________________