adl5336 Analog Devices, Inc., adl5336 Datasheet - Page 17

• Manufacturer Part Number: adl5336
• Description: Cascadable If Vgas With Programmable Rms Detectors
• Manufacturer: Analog Devices, Inc.

THEORY OF OPERATION
CIRCUIT DESCRIPTION
The
programmable, internally connected, square law detector. VGA2
includes an input select switch that allows the user to choose
between two sets of differential inputs.
The signal path of each VGA, shown in Figure 59 and Figure 60,
consists of a variable input attenuator followed by a programmable
gain amplifier (PGA).
The input attenuator is built from an 18-section resistor ladder,
providing 1.34 dB of attenuation at each successive tap point.
The resistor ladder acts as a linear input attenuator, in addition
to providing an accurate 200 Ω input impedance. The variable
transconductance (g
signal from the appropriate tap point along the ladder and feed
this signal to the fixed gain amplifier. To realize a continuous
gain control function from discrete tap points, the gain interpolator
creates a weighted sum of signals appearing on adjacent tap points
by carefully controlling the variable g
ADL5336
contains two differential VGAs, each with a
m
) stages are used to select the attenuated
IM2A
IM2B
IP2A
IP2B
GAIN1
INM1
INP1
m
stages.
GAIN2
200Ω
0dB
200Ω
Figure 59. VGA1 Functional Block Diagram
Figure 60. VGA2 Functional Block Diagram
GAIN INTERPOLATOR
ATTENUATOR LADDER
0dB
–1.4dB
g
m
GAIN INTERPOLATOR
ATTENUATOR LADDER
STAGES
MODE
Rev. A | Page 17 of 32
–1.4dB
g
m
–2.8dB
STAGES
MODE
–2.8dB
–22.4dB
The weighted sum of the different tap points is fed into the
programmable gain stage. The programmable gain stage achieves
its different gain settings by changing the feedback network of
the amplifier.
The input attenuator and g
of 24 dB, whereas the programmable gain amplifier sets the
maximum gain of each VGA.
Table 4. VGA Gain Range
VGA1
0
0
1
1
Maximum Gain Word
–22.4dB
–23.8dB
PGA
VGA2
0
1
0
1
PGA LINEAR
VOLTAGE GAIN:
G = 3, 4, 5, 6
–23.8dB
PGA LINEAR
VOLTAGE GAIN:
G = 5, 7, 9, 11
PGA
OPP1
OPM1
VGA1 Range (dB)
−14.5 to +9.5
−12 to +12.0
−10 to +14.0
−8.4 to +15.6
OPP2
OPM2
m
stages provide analog gain control
VGA2 Range (dB)
−10 to +14
−7.1 to +16.9
−5 to +19
−3.1 to +20.9
ADL5336