The sample rate for
is 1Msps and the sample
is 1.6Msps, the MAX11905’s maximum
sample rate. As measured at the MAX11905 output, the
signal-to-noise ratio is > 97dB for both sample rates, with
total harmonic distortion > 112.9dB.
Figures 11 to 13 detail the DC performance of the
MAX44206 and MAX11905. These three figures detail
the results of shorting the inputs together to GND at the
sources and measuring the noise histogram at the
output of the ADC. All data was measured at 1Msps, with
65,536 samples taken.
shows the results at a
20-bit code level with no averaging. Effective number of
bits (ENOB) is 17.9 bits.
One technique to improve a system’s ENOB is to aver-
age multiple samples. The tradeoff is a reduced effective
sample rate. The theoretical expected results of averag-
ing are a 0.5 improvement in ENOB for every average
factor of 2. Therefore, averaging by 16x should improve
ENOB by 2 bits.
details this example, and the
ENOB is improved nearly 2 bits, from 17.9 bits to 19.8
bits. This shows that the noise from the ADC and the op
amp are not limiting the ENOB.
shows the results of averaging by 64x, which
will limit the effective sample rate to 15.6ksps (1Msps/64).
ENOB is 20.8 bits in this mode, making the MAX11905 a
lower power alternative to high-speed 24-bit delta-sigma
Figure 9. MAX11905 FFT (fSAMPLE = 1Msps, fIN = 10kHz)
180MHz, Low-Noise, Low-Distortion, Fully
Differential Op Amp/ADC Driver
Maxim Integrated │