MICROWAVE CORPORATION
HMC173MS8
HMC173MS8 VOLTAGE VARIABLE ATTENUATOR 800-2000 MHz
F
EBRUARY
2001
Attenuation Linearizing Control Circuit For The
HMC173MS8 Voltage Variable Attenuator
A driver circuit to improve the attenuation linearity of the HMC173MS8 can be implemented with a simple op-amp
configuration. A
breakpoint
linearization circuit will scale the voltage supplied to the control line of the HMC173MS8,
so that a more linear attenuation vs. control voltage slope can be achieved. A -5V and +5V supply is required.
2
SMT A
TTENUATORS
Diode and resistor values which define the op-amp gain, and breakpoint were selected to optimize a measured
production lot of attenuators at 825 MHz. R7 may be varied to optimize the performance of any given attenuator. If the
input voltage to the linearizing circuit will not drop below 1.0V, then R9 and D2 may be omitted, and this will greatly reduce
the overall power consumption of the driver circuit.
The linearizing circuit has been optimized for 825 MHz attenuation applications. A similar approach may be used at other
frequencies by adjusting RI - R9 resistor values.
Required Parts List
Part
AD822
R1
R2
R3
R4
R5
R6
R7
R8
R9
D1, D2
Schematic
0
+5V
R6
R5
VCTL IN
R8
0
R7
R1
3
Description
Op-Amp
10K ohms
200K ohms
7.5K ohms
39K ohms
220K ohms
91K ohms
910 ohms
51 ohms
100 ohms
LL4148 D-35
Manufacturer
Analog Devices
Panasonic
Panasonic
Panasonic
Panasonic
Panasonic
Panasonic
Panasonic
Panasonic
Panasonic
Digikey
+5
-5V
D1
R4
R9
7
U3
6
+
V+
AD820/AD
2 _ V-
4
D2
VCTL OUT
-5V
R2
R3
Return Loss vs. Control Voltage
@ 825 MHz
-12
-13
RETURN LOSS (dB)
Attenuation vs. Control Voltage
@ 825 MHz
0
-10
Without
Linearizer
With
Linearizer
-14
-15
-16
-17
-18
-19
0.5
1
1.5
With
Linearizer
Without
Linearizer
ATTENUATION (dB)
-20
-30
-40
-50
-60
2
2.5
3
0
1
2
3
CONTROL VOLTAGE (Vdc)
CONTROL VOLTAGE (Vdc)
12 Elizabeth Drive, Chelmsford, MA 01824
Phone: 978-250-3343
Fax: 978-250-3373
Web Site: www.hittite.com
2 - 30
HITTITE [ HITTITE MICROWAVE CORPORATION ]
