Rainbow Electronics MAX5858 - Manual (Page 14)

MAX5858
Dual, 10-Bit, 300Msps, Current-Output DAC with
4x/2x/1x Interpolation Filters
14 ______________________________________________________________________________________
Device Power-Up and
States of Operation
At power-up, the MAX5858’s default configuration is
no-interpolation mode with a gain of 0dB and a fully
operational converter. In shutdown, the MAX5858 con-
sumes only 1µA of supply current, and in standby the
current consumption is 4.4mA. Wake-up time from
standby mode to normal operation is 0.7µs.
Interpolation Filters
The MAX5858 features a two stage, 2x digital interpo-
lating filter based on 43-tap and 23-tap FIR topology.
F1EN and F2EN enable the interpolation filters. F1EN
high enables the first filter for 2x interpolation and F2EN
high enables the second filter for combined 4x interpo-
lation. To bypass and disable both interpolation filters
(no-interpolation mode or 1x mode) set F1EN = F2EN =
0. When set for 1x mode the filters are powered down
and consume virtually no current. An illegal condition is
defined by: F1EN = 0, F2EN = 1 (see Table 2 for con-
figuration modes).
The programmable interpolation filters multiply the
MAX5858 input data rate by a factor of 2x or 4x to sep-
arate the reconstructed waveform spectrum and the
first image. The original spectral images, appearing
around multiples of the DAC input data rate, are attenu-
ated at least 60dB by the internal digital filters. This fea-
ture provides three benefits:
1) Image separation reduces complexity of analog
reconstruction filters.
2) Lower input data rates eliminate board level high-
speed data transmission.
3) Sin(x)/x roll-off is reduced over the effective band-
width.
Figure 2 shows an application circuit and Figure 3 illus-
trates a practical example of the benefits when using
the MAX5858 in 4x-interpolation mode. The example
illustrates signal synthesis of a 20MHz IF with a
±10MHz bandwidth. The designer can consider three
options to address the design challenge. The tradeoffs
for each solution are depicted in Table 4.
CONTROL WORD FUNCTION
PD Power-Down. The part enters power-down mode if PD = 1.
DACEN DAC Enable. When DACEN = 0 and PD = 0, the part enters standby mode.
F2EN
Filter Enable. When F2EN = 1 and F1EN = 1, 4x interpolation is enabled. When F2EN = 0, the interpolation
mode is determined by F1EN.
F1EN
Filter Enable. When F1EN = 1 and F2EN = 0, 2x interpolation is active. With F1EN = 0 and F2EN = 0, the
interpolation is disabled.
G3 Bit 3 (MSB) of Gain Adjust Word.
G2 Bit 2 of Gain Adjust Word.
G1 Bit 1 of Gain Adjust Word.
G0 Bit 0 (LSB) of Gain Adjust Word.
Table 1. Control Word Format and Function
MODE PD DACEN F2EN F1EN
No interpolation 0 1 0 0
2x interpolation 0 1 0 1
4x interpolation 0 1 1 1
Standby 0 0 X X
Power-down 1 X X X
Power-up 0 1 X X
Table 2. Configuration Modes
GAIN ADJUSTMENT ON
CHANNEL A (dB)
G3 G2 G1 G0
+0.4 0 0 0 0
0 1 0 0 0
-0.35 1 1 1 1
Table 3. Gain Difference Setting
X = Don’t care.
F1EN = 0, F2EN = 1 illegal.
MSB LSB
PD DACEN F2EN F1EN G3 G2 G1 G0 X X