Rainbow Electronics MAX1011 - Manual (Page 9)

______________Dynamic Performance
Signal-to-noise and distortion (SINAD) is the ratio of the
fundamental input frequency’s RMS amplitude to all
other ADC output signals. The output spectrum is limit-
ed to frequencies above DC and below one-half the
ADC sample rate.
The theoretical minimum analog-to-digital noise is
caused by quantization error, and results directly from
the ADC’s resolution: SNR = (6.02N + 1.76)dB, where
N is the number of bits of resolution. Therefore, a per-
fect 6-bit ADC can do no better than 38dB.
The FFT Plot (see Typical Operating Characteristics )
shows the result of sampling a pure 20MHz sinusoid at
a 90MHz clock rate. This FFT plot of the output shows
the output level in various spectral bands. The plot has
been averaged to reduce the quantization noise floor
and reveal the low-amplitude spurs. This emphasizes the
excellent spurious-free dynamic range of the MAX1011.
The effective resolution (or effective number of bits) the
ADC provides can be measured by transposing the
equation that converts resolution to SINAD: N = (SINAD
- 1.76)/ 6.02 (see
Typical Operating Characteristics ).
MAX1011
Low-Power, 90Msps, 6-Bit ADC
_______________________________________________________________________________________ 9
Figure 9. Ideal Transfer Function
111111
OUTPUT CODE
111110
111101
100001
100000
011111
011110
000011
000010
000001
000000
-FSR
2
0
1LSB
INPUT VOLTAGE (IN+ TO IN-)
FSR
2
Figure 8. MAX1011 Timing Diagram
DATA OUT 1.4V DATA VALID N - 1 DATA VALID N
1.4V
50%
t SKEW
t DCLK
t AD
t PD
TNK+
(INPUT CLOCK)
DCLK
ANALOG
INPUT
N
N + 1
N + 2