Rainbow Electronics MAX1201 - Manual (Page 12)

M
A
X12
01
+5V Single-Supply, 2.2Msps, 14-Bit
Self-Calibrating ADC
12 ______________________________________________________________________________________
Table 1. Binary Output Codes
Signal-to-Noise
Plus Distortion (SINAD)
SINAD is the ratio of the fundamental input frequency’s
RMS amplitude to all other ADC output signals.
SINAD (dB) = 20 · log [Signal RMS / (Noise +
Distortion) RMS ]
Effective Number of Bits (ENOB)
ENOB indicates the global accuracy of an ADC at a
specific input frequency and sampling rate. An ideal
ADC’s error consists only of quantization noise. With an
input range equal to the full-scale range of the ADC, the
effective number of bits can be calculated as follows:
ENOB = (SINAD - 1.76) / 6.02
Total Harmonic Distortion (THD)
THD is the ratio of the RMS sum of the first nine har-
monics of the input signal to the fundamental itself. This
is expressed as:
where V 1 is the fundamental amplitude, and V 2 through
V 9 are the amplitudes of the 2nd through 9th-order har-
monics.
Spurious-Free
Dynamic Range (SFDR)
SFDR is the ratio of RMS amplitude of the fundamental
(maximum signal component) to the RMS value of the
next largest spurious component, excluding DC offset.
Grounding and Power-Supply Decoupling
Grounding and power-supply decoupling strongly influ-
ence the performance of the MAX1201. At 14-bit reso-
lution, unwanted digital crosstalk may couple through
the input, reference, power supply, and ground con-
nections; this adversely affects the signal-to-noise ratio
or spurious-free dynamic range. In addition, electro-
magnetic interference (EMI) can either couple into or
be generated by the MAX1201. Therefore, grounding
and power-supply decoupling guidelines should be
closely followed.
First, a multilayer, printed circuit board (PCB) with sep-
arate ground and power-supply planes is recommend-
ed. Run high-speed signal traces on lines directly
above the ground plane. Since the MAX1201 has sepa-
rate analog and digital ground buses (AGND and
DGND, respectively), the PCB should also have sepa-
rate analog and digital ground sections connected at
only one point (star ground). Digital signals should run
above the digital ground plane and analog signals
should run above the analog ground plane. Digital sig-
nals should be kept far away from the sensitive analog
inputs, reference input senses, common-mode input,
and clock input.
THD 20 log
V
V
2
2
V V V
=
( ) 











⋅
+ + + ⋅ ⋅ ⋅ +
3
2
4
2
9
2
1
SCALE OFFSET BINARY ONE’S COMPLEMENT TWO’S COMPLEMENT
+FSR - 1LSB 1111 .... 1111 0111 .... 1111 0111 .... 1111
+3/4FSR 1110 .... 0000 0110 .... 0000 0110 .... 0000
+1/2FSR 1100 .... 0000 0100 .... 0000 0100 .... 0000
+1/4FSR 1010 .... 0000 0010 .... 0000 0010 .... 0000
+0 1000 .... 0000 0000 .... 0000 0000 .... 0000
-0 —— .... —— 1111 .... 1111 —— .... ——
-1/4FSR 0110 .... 0000 1101 .... 1111 1110 .... 0000
-1/2FSR 0100 .... 0000 1011 .... 1111 1100 .... 0000
-3/4FSR 0010 .... 0000 1001 .... 1111 1010 .... 0000
-FSR +1LSB 0000 .... 0001 1000 .... 0000 1000 .... 0001
-FSR 0000 .... 0000 —— .... —— 1000 .... 0000