Datasheet

MAX2066
50MHz to 1000MHz High-Linearity,
Serial/Parallel-Controlled Digital VGA
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Table 2. SPI Data Format (continued)
FUNCTION BIT DESCRIPTION
D7
D6
D5
D4
D3
D2
D1
Reserved
D0 (LSB)
Bits D[7:0] are reserved. Set to logic 0.
Digital Attenuator Settings
Using the Parallel Control Bus
To capitalize on its fast 25ns switching capability, the
MAX2066 offers a supplemental 5-bit parallel control
interface. The digital logic attenuator-control pins
(D0–D4) enable the attenuator stages (Table 3).
Direct access to this 5-bit bus enables the user to avoid
any programming delays associated with the SPI
interface. One of the limitations of any SPI bus is the
speed at which commands can be clocked into each
peripheral device. By offering direct access to the 5-bit
parallel interface, the user can quickly shift between
digital attenuator states as needed for critical “fast-
attack” automatic gain-control (AGC) applications.
“Rapid-Fire” Preprogrammed
Attenuation States
The MAX2066 has an added feature that provides
“rapid-fire” gain selection between four prepro-
grammed attenuation steps. As with the supplemental
5-bit bus mentioned above, this “rapid-fire” gain selec-
tion allows the user to quickly access any one of four
customized digital attenuation states without incurring
the delays associated with reprogramming the device
through the SPI bus.
The switching speed is comparable to that achieved
using the supplemental 5-bit parallel bus. However, by
employing this specific feature, the digital attenuator
I/O is further reduced by a factor of either 5 or 2.5 (5
control bits vs. 1 or 2, respectively) depending on the
number of states desired.
The user can employ the STATE_A and STATE_B logic-
input pins to apply each step as required (Table 4).
Toggling just the STATE_A pin (one control bit) yields
two preprogrammed attenuation states; toggling both
the STATE_A and STATE_B pins together (two control
bits) yields four preprogrammed attenuation states.
Table 3. Digital Attenuator Settings (Parallel Control)
INPUT LOGIC = 0 (OR GROUND) LOGIC = 1
D0 Disable 1dB attenuator, or when SPI is default programmer Enable 1dB attenuator
D1 Disable 2dB attenuator, or when SPI is default programmer Enable 2dB attenuator
D2 Disable 4dB attenuator, or when SPI is default programmer Enable 4dB attenuator
D3 Disable 8dB attenuator, or when SPI is default programmer Enable 8dB attenuator
D4 Disable 16dB attenuator, or when SPI is default programmer Enable 16dB attenuator