Rainbow Electronics MAX5858 - Manual (Page 16)

MAX5858
Dual, 10-Bit, 300Msps, Current-Output DAC with
4x/2x/1x Interpolation Filters
16 ______________________________________________________________________________________
f OUT
20MHz ±10MHz
IMAGE
f DAC - f OUT
48MHz
IMAGE
f DAC + f OUT
108MHz
f DAC
78MHz
IMAGE SEPARATION = 18MHz
LESS THAN ONE OCTAVE
HIGH ORDER ANALOG FILTER
SOLUTION 1
f OUT
20MHz
BW = ±10MHz
IMAGE
f DAC - f OUT
210MHz
IMAGE
f DAC + f OUT
270MHz
f DAC
240MHz
LOWER ORDER
ANALOG FILTER
IMAGE SEPARATION = 180MHz
HIGH-SPEED CLK = 240MHz
SOLUTION 2
FREQUENCY AXIS NOT TO SCALE
f OUT
20MHz
BW = ±10MHz
IMAGE
f DAC - f OUT
256MHz
IMAGE
f DAC + f OUT
316MHz
f DAC
286MHz
f DATA
71.6MHz
SIMPLE ANALOG FILTER
NEW FIRST IMAGE SEPARATION > 3 OCTAVES
SOLUTION 3
FREQUENCY AXIS NOT TO SCALE
FREQUENCY AXIS NOT TO SCALE
DIGITAL FILTER
ATTENUATION >60dB
Figure 3. MAX5858 in 4x Interpolation Mode
This example demonstrates that 4x interpolation with
digital filtering yields significant benefits in reducing
system complexity, improving dynamic performance
and lowering cost. Data can be written to the MAX5858
at much lower speeds while achieving image attenua-
tion greater than 60dB and image separation beyond
three octaves. The main benefit is in analog reconstruc- tion filter design. Reducing the filter order eases
gain/phase matching while lowering filter cost and sav-
ing board space. Because the data rate is lowered to
71.6MHz, the setup and hold times are manageable
and the clock signal source is simplified, which results
in improved system reliability and lower cost.