ammp-6650 Avago Technologies, ammp-6650 Datasheet - Page 8
ammp-6650
Manufacturer Part Number
ammp-6650
Description
Dc ? 30 Ghz Variable Attenuator
Manufacturer
Avago Technologies
Datasheet
1.AMMP-6650.pdf
(12 pages)
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
ammp-6650-BLKG
Manufacturer:
AVAGO/安华高
Quantity:
20 000
Part Number:
ammp-6650-TR1G
Manufacturer:
AVAGO/安华高
Quantity:
20 000
Biasingconsiderations
RFin
Note : Package base : GND
Figure13.Biasvoltageconnections
Attenuation is controlled by applying voltage to pin V1
(Pin 7) and pin V2 (Pin5), as shown in Figure 13.
For the minimum attenuation, V1 is set to 1.5 V and V2
is set to 0 V. The 1.5 V applied to the V1 pin biases the
series FETs to a full “on” state, while the 0 V applied to the
V2 pin keeps the shunt FETs in an “off” or “open” state;
thus creating the lumped element 50 Ω transmission line
effect. The V2 voltage swing from 0 V to 1.25 V increases
the level of attenuation. The V1 voltage swing from 1.5 V
to 0 V effectively optimizes the input and output match at
higher attenuation levels. The AMMP-6650 can be driven
by two complementary voltage ramps placed on V1 and
V2. Careful adjustments of the two control lines over a
relatively small voltage ranges are required to set the at-
tenuation and optimize VSWR.
The on-chip DC reference circuit can be used to optimize
VSWR for any attenuation setting, improve voltage versus
attenuation linearity and range, and provide temperature
compensation.
The on-chip DC reference circuit is a non-distributed “T”
attenuator designed to operate in a 500 Ω system and
track the control voltage versus attenuation character-
istics of the RF attenuator. A simplified schematic of the
AMMP-6650 together with an op-amp driver that utilizes
the DC reference circuit is shown in Figure 14.
OP AMP 1 insures that the attenuator maintains a good
input and output match to 50 Ω, while OPAMP2 increases
the usable control voltage range versus using only direct
voltage ramps for V1 and V2 and improves over tempera-
ture operation.
8
8
DCin
V1
1
7
reference circuit
attenuator
Top View
variable
NC
NC
DC
2
6
DCout
V2
5
3
4
RFout
Pin
Pin
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
Function
Function
DC out
DC out
RF out
RF out
DC in
DC in
RF in
RF in
V2
V2
V1
V1
R
Figure14.AMMP-6650andtheop-ampdrivercircuit
If optimum VSWR is all that is required, OPAMP2 may be
eliminated however, R
DCout pad of the AMMP-6650 and the control voltage can
be applied directly to V2.
CAUTION: Low voltage op-amps must be used so as not to
exceed the maximum limit of V1 and V2 control voltages.
As shown, a voltage reference (V
circuit DCin pad via a 500 Ω resistor, creating a 500 Ω
source. The reference circuit termination R
to the DCout pad and ideally is also equal to 500 Ω. This
voltage is controlled in parallel with the RF attenuator.
The chosen value of V
modifying the FET biasing and lower than the turn-on
voltage of the ESD protection diode but high enough such
that the attenuated voltage at OPAMP2 is usable compared
to input offsets etc. The optimum value for the positive
reference voltage is approximately 0.1 to 0.4 V.
At equilibrium, the voltages at nodes A and B of the
OP AMP 1 must be equal which implies that the input
impedance to the DC reference circuit is equal to R
When V2 is changed to a lower value, the voltage at node
A becomes greater than that of node B. This voltage dif-
ference causes the output voltage of op OP AMP 1 to
move toward its positive rail until equilibrium is once
again established. When V2 is changed to a higher value
the voltage at node A becomes less than that of node B
and the output voltage of OPAMP1 will swing toward its
negative rail until equilibrium is reached. If the reference
circuit precisely tracks the RF circuit, the voltage output
of OP AMP 1 at equilibrium insures that the RF circuit is
matched to 50 Ω.
V
REF
REF
(620)
500
R
500
S
A
B
RFin
OP AMP 1
+
_
C1
DCin
V1
REF
L
NC
NC
must remain connected to the
must be low enough to avoid
V2
REF
DCout
) is fed to the reference
OP AMP 2
RFout
+
_
C
D
L
, is connected
R
R1 (10K)
R2 (100)
L
V
(500)
CONTROL
REF
.