M521 MA-COM [M/A-COM Technology Solutions, Inc.], M521 Datasheet - Page 2

• Manufacturer Part Number: M521
• Description: Positive Voltage Control of GaAs MMIC Control Devices
• Manufacturer: MA-COM [M/A-COM Technology Solutions, Inc.]

2
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Positive Voltage Control of
GaAs MMIC Control Devices
Application Note
M521
Applications
This type of voltage floating technique can be used
in most control component applications. A typical
switch and digital attenuator application are pre-
sented in Figure 2. Each application is similar in
that the source of the FET’s are biased at +5 V and
the gates can be controlled by 0 and +5 V.
In all cases, the ground pins which have a source
connection must be AC coupled with the shortest
possible path to ground.
The AT-210 is shown as an example of a digital
attenuator which is floated. Pins 10 through 15 are
normally grounded, but in this case are floated to
the +5 V supply and AC coupled to ground. One of
the RF connections must also be tied to +5 V to
ensure the source of the series FET’s are floated.
As mentioned above, all efforts to minimize induc-
tance to ground must be taken to ensure the full
attenuation range of the device. A truth table for
the digital attenuator in the floated configuration is
shown in Table 1.
Positive Voltage Control Configuration
SW-239 with +5 V Supply
of the SW-239
Figure 2b.
The SW-239 is shown as an example of a SPDT
switch which is floated using this technique. Pins
2, 7, and 8 are normally ground and must be
floated with +5 V as well as being AC coupled to
ground. A +5 V supply is also required at the RF
common to ensure that the source of the series
FET’s are floated. The resistors R1 and R3 will
result in slower switching speed, but will minimize
coupling of RF signals along the +5 V line. A truth
table for this device in the floated configuration is
given in Table 2.
VC4 VC4 VC3 VC3 VC2 VC2 VC1 VC1
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Control A
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
+5 V
0 V
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
AT-210 Truth Table (+5 V Control)
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
Control Inputs
Control B
SW-239 Truth Table
+5 V
0 V
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
Table 1.
Table 2.
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
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1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
OFF
RF1
ON
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
OFF
RF2
ON
Rev. V3
Attn
(dB)
Ref.
10
11
12
13
14
15
1
2
3
4
5
6
7
8
9