AD8309 Analog Devices, AD8309 Datasheet - Page 19

• Manufacturer Part Number: AD8309
• Description: 5 - 500 Mhz, 100 DB Demodulating Logarithmic Amplifier With Limiter Output
• Manufacturer: Analog Devices

Component
SW1
R1
R/L, C1, C2
R3/R4
L1, C5, C6
R8, LK1
C7
REV. B
Figure 41. Layout of Signal Layer
Function
Device Enable. When in position A, the ENBL pin is connected to +V
AD8309 is in normal operating mode. In position B, the ENBL pin is connected
to an SMA connector labeled Ext Enable. An applied signal can be applied to this
connector to enable/disable the AD8309. If left open, the ENBL pin will float to
ground putting the device in power-down mode.
This pad is used to ac-couple to ground for single-ended input drive. To drive the
AD8309 differentially, R1 should be removed.
Input Interface. The 52.3
a high pass input filter whose corner frequency (640 kHz) is equal to 1/( RC),
where C = C1 = C2 and R is the parallel combination of 52.3
input impedance of 1000 . Alternatively, the 52.3
an inductor to form an input matching network. See Input Matching Network
section for more details.
Slope Adjust. A simple slope adjustment can be implemented by adding a resistive
divider at the VLOG output. R3 and R4, whose sum should be about 1 k , and
never less than 40
Slope = 20 mV/dB
Limiter Output Coupling. C5 and C6 ac-couple the limiter’s differential outputs.
By adjusting these values and installing an inductor in L1, an output matching
network can be implemented.
Limiter Output Current. With LK2 installed, R8 enables and sets the limiter
output current. The limiter’s output current is set according to the equation
(I
To disable the limiter (recommended if the limiter is not being used), LK3 should
be removed.
RSSI Bandwidth Adjust. The addition of C7 will lower the RSSI bandwidth of the
VLOG output according to the equation: f
OUT
= 400 mV/R8). The limiter current can be as high as 10 mA (R8 = 40 ).
R4/(R3+R4).
(see specs), set the slope according to the equation:
Table IV. Evaluation Board Setup Options
resistor in position R/L along with C1 and C2 create
CORNER
–19–
= 12.7
resistor can be replaced by
10
–
6/(C
Figure 42. Layout of Power Layer
and the AD8309’s
FILT
S
+ 3.5 pF).
and the
Default Condition
SW1 = A
R1 = 0
R/L= 52.3
C1 = C2 = 0.01 F
R3 = 0
R4 =
L1 = Open
C5 = 0.01 F
C6 = 0.01 F
LK1 Installed. R8 = 402
C7 = Open
AD8309