TGS2304-SCC View Datasheet(PDF) - TriQuint Semiconductor
Part Name
Description
MFG CO.
'TGS2304-SCC' PDF : 18 Pages View PDF
Product Data Sheet
TGS2304-SCC
Application Notes: Driver Circuit for 2300 Series GaAs PIN Diode Switches
INTRODUCTION
This section describes how a single 5 V power supply and a 74F24ON line driver
are used in a driver circuit for the TGS2304 PIN-diode switch. The PIN switch
must be mounted on a silicon MOS capacitor (MOSCAP or equivalent) of
approximately 1000 pF (see Mounting Diagram, page 15). Eight separate drivers
are provided in a single ‘F240 DIP (see Driver Circuit, page 15). In addition, the
‘F240 can be set to provide an inverted or a non-inverted output. The inverted is
preferred in this application because it allows the 1G pin to be tied to ground
instead of 5 V, eliminating the use of an extra power supply. The 74BCT240,
74BCT240N, and 74S240N also work with this driver circuit.
CONNECTION
INSTRUCTIONS
The Interface Schematic (see page 16) shows a voltage divider that can be used
to provide approximately 2 V to the RF Input (common) port of the TGS2304-SCC.
This bias voltage should be connected to the RF Input through a bias tee or some
equivalent RF choke/DC block network.
Connect this same bias voltage to the top plate of the MOSCAP through a ~3-nH
coil bonded to MMIC ground pad as shown in the Interface Schematic and RF
Input Bias Coil Assembly (both on page 16). Care should be taken not to bond the
inductor close to the via, as this could result in device damage. The ground pad is
connected to the backside of the TGS2304-SCC by plated-through vias. This sets
the top plate of the MOSCAP to 2 V, effectively providing a 2 V reference for the
RF input port and the cathodes of the two shunt diodes in each arm. The bottom
plate of the MOSCAP is true DC ground.
Connect the four RF Output ports of the TGS2304-SCC to the ‘F240 outputs
through a bias tee or some equivalent RF choke/DC block, as shown in the
Interface Schematic on page 16.
OPERATING
INSTRUCTIONS
For proper switch operation, only one arm should be turned on at any one time as
shown in the Control Logic Table on page 15. The following description of how the
driver circuit controls one arm of the TGS2304-SCC applies to all arms.
To turn an arm on: A TTL high at the ‘F240 input results in approximately 0.3 V at
the corresponding output. This is applied to the appropriate RF Output port. Since
the RF Input port of the TGS2304-SCC is at 2 V, the arm is turned on. The series
diode in that arm is forward biased by approximately 1.7 V, and the two shunt
diodes are reverse biased (off) by 1.7 V. Under these conditions, the bias current
is typically 12 mA and midband insertion loss is typically 0.9 dB.
To turn an arm off: A TTL low at the ‘F240 input results in approximately 3.1 V at
the corresponding output. This is applied to the appropriate RF Output port. Since
the RF Input port of the TGS2304-SCC is at 2 V, the arm is turned off. The series
diode in that arm is reverse biased by approximately 1.1 V, and the shunt diodes
in that arm are forward biased (on) by 1.1 V. Under these conditions, the bias
current is typically 9 mA and the midband isolation is typically 40 dB.
TriQuint Semiconductor Texas Phone: (972)994 8465 Fax: (972)994 8504 Web: www.triquint.com
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