Datasheet

AD8366
Rev. A | Page 16 of 28
GAIN CONTROL INTERFACE
The AD8366 provides two methods of digital gain control:
serial or parallel. When the SENB pin is pulled low, the part
is in parallel gain control mode. In this mode, the two digitally
controlled VGAs can be programmed simultaneously, or one at
a time, depending on the levels at DENA and DENB. If the SENB
pin is pulled high, the part is in serial gain control mode, with
Pin 24, Pin 23, and Pin 22 corresponding to the CS, SDAT, and
SCLK signals, respectively.
The voltage gain of the AD8366 is well approximated by
Gain (dB) = GainCode × 0.253 + 4.5
Note that at several major transitions (15 to 16, 31 to 32, and 47 to
48), the gain changes significantly less (0 dB step) or significantly
more (0.5 dB step) than the desired 0.25 dB step. This is inherent
in the design of the part and is related to the partitioning of the
variable gain block into a fine-gain and a coarse-gain section.
–1.0
–0.8
–0.6
–0.4
–0.2
0
0.2
0.4
0.6
0.8
1.0
0
2.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0
22.5
25.0
0 5 10 15 20 25 30 35 40 45 50 55 60
GAIN STEP ERROR (dB)
GAIN (dB)
GAIN CODE
07584-063
Figure 49. Gain and Gain Step Error vs. Gain Code at 10 MHz