amplifier design
Post on 08-Jan-2016
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ACTIVE MW CKTS
Oscillators, Amplifiers and Mixers
Design is tough
Bias network is required,
Devices are nonlinear,
Unintended oscillations produced by circuit instability
AC > 1
PC < 1, S parameters with magnitudes greater than unity are physically impossible
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MWA
Heart of RF and MW systems
MWA
Tubes Klystrons and TWT
Solid-state Tunnel or varactor diodes
Today Transistor devices such as Si BJTs, GaAs or SiGe HBTs, Si MOSFETs, GaAs MESFETs, or GaAs or GaN HEMTs
Adv Rugged, low-cost, and reliable and can be easily integrated in ICs
Req. small size, low noise figure, broad bandwidth, and medium to high power capacity
IMP G, Stability, Noise figure (NF), Noise Factor (F)
Degradation of the SNR
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MICROWAVE AMPLIFIER - GAINS
Two port gains, by definitions
Transducer power gain
Power gain
Available power gain
PL PAVS PIN PAVN
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These three definitions of power gain are used to
design different types of amplifiers:
Operating Power Gain, G. Maximum linear output power
amplifiers
Available Power Gain, GA Low Noise Amplifiers (LNAs)
Transducer Power Gain, GT, Simultaneously conjugate
matched input and output ports (leads to maximum linear
gain)
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1. 3 factors how power G red. By S & L ckts
2. G not dep , 3. both 4. If S & L are both
conjugate matched
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Passive Unit: Dealt with the
matching properties at input Passive Unit: Dealt with the
matching properties at output
Gain of Transistor
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STABILITY
The quality of being stable
Ability of a substance to remain unchanged over time
An amplifier circuit has gain G and if its not properly designed, it may oscillate
It is referred to as circuit stability
A brief period of oscillation could permanently
damage a circuit
Since large V and P levels that might be generated
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TYPES OF STABILITY
Unconditionally stable:
in
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STABILITY CONDITIONS
Here if transistor is unilateral:
S12= 0, then in , out are just S11 and S22.
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STABILITY CIRCLES
It can be very helpful to generate a graphical
depiction of the range of and values that may lead to instability
Stability circles define the boundary between
stable and potentially unstable and
1. Center
2. Radius
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STABILITY TESTS
K- test: For unconditionally stable
test:
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If >1, the device is unconditionally stable This is the mu stability factor. Larger values of imply greater stability.
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STABILITY REGIONS
Boundary of Stability circle is in=1.
Stable region For S11 < 1 For S11 >1
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Unconditionally stable
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