Amplifiers
• Gain = Po/Pi in dB = 10 log (Po/Pi) • Gain Flatness (Gian Ripple vs. frequency) “the maximum deviation of
the gain over specified frequency range”• Gain Variation vs. Temperature• 1 dB Output Compression point• Noise Figure• Efficiency • Bandwidth• Limited Power Output• Third Order Output Intercept Point• Second Order Output Intercept Point• VSWR (Voltage Standing Wave Ratio), Return Loss• Reverse Isolation (output to input)
Amplifier Parameters
Amplifier Gain Flatness
Amplifier Gain Variation vs. Temperature
1 dB Output Compression Point
The 1dB Compression output point is used to specify the power output capability of an amplifier
30
20
10
0
-10
Pout (dBm)
-30 -20 -10 0 10 Pin (dBm)
1 dB compression point
Power Gain:
Gain = Pout/Pin
Gain (dB) =
Pout - Pin (dBm)
Gain changes with output power level.
Linear gain
Saturation gain
Efficiency: = Pout/(Pdc in + Pin) Power added efficiency
Bandwidth: BW = (fH-fL)/fM
fM = (fH-fL)/2
Amplifier Noise Figure (NF) or F
An ideal amplifier adds no noise to the signal being amplified. However, all practical amplifiers generate noise.
(S/N)i
(S/N)o
F = No
GNi
=
The Noise Figure of the amplifier in most cases determines the sensitivity of the receiver.
• Intercept Points are located in the non-lnear portion (amplifier in saturation) of the Pi vs. Po curve
• Intermodulation occurs when two or more signals are present simultaneously.In the non-linear region, the relationship between the input and output of anamplifier can be written as
Vo = a1Vi + a2Vi2 + a3Vi
3 + ...where Vo and Vi are the output and input voltage of the amplifier; a1, a2, etc. are the coefficients•The second order term( a2Vi
2 creates second order intermodulation
•The third order intercept point (a3Vi3 creates third order intermodulation
Intercept Points
Intercept Points Cont.
Harmonic and spurious response:
Fundamental 2nd Harmonic~ 10 dB below fund. at sat
3rd Harmonic
Spurious 10 dB below fund
White noise
Frequency
Power
Intermodulation product:
Ripple componentsin RF out(-60dBc)
Types of Microwave Semiconductor Amplifiers
Power Amplifiers LNA
LNA Design
(1) Select transistor [S-and Noise parameters)
(2) Stability analysis
(3) Find appropriate load and source impedance
(4) Design matching and biasing networks
(5) Check out-of-band stability (suitable simulator is recommended)
(6) Realization
(7) Measurements
(8) Adjustment and correction
Power Amplifier Design
(1) Select transistor (Frequency – Power- non-linear parameters)
(2) Choose class of operation (A, AB, B, C, D,….) and then appropriate bias condition
(2) Non-linear characterization
(3) Find appropriate load and source impedances
(4) Design matching and biasing networks
(5) Check out-of-band stability (suitable simulator is recommended)
(6) Realization
(7) Measurements
(8) Adjustment and correction
15
20
25
30
0 5 10 15 20
0
10
20
30
40
50
60
70
80
ps
rend
25
0
-25
25
0
-25
Le gain à 1.64 GHz est de 16.61 dB
S11 (dB)
S21
1,4 1,8 Freq. GHz
Single GaAs FET Amplifier
Gain per stage 5-6 dB PA to 10-12 dB LNA
•Output 1dB Compression Point
LNA < + 10 dBm
Med PA +18 dBm to 21 dBm
•Output Third Order Intercept Point
Typically 8-10 dB above the 1 dB Compression Point
•Output Second Order Intercept Point
Typically 8-10 dB above the output third order intercept point
•Saturation Level
Typically 3-6 dB above the 1dB compression point
3 dB for medium to high power amplifier
5-6 dB for low noise amplifier
Amplifier Temperature Effect and Compensation
• For a single stage amplifier
Typical amplifier gain changes are plus and minus 1dB from room temperature (~ 0.015 dB/oC per stage)
Gain decreases 1dB per stage for ( +25oC to 95oC)
Gain increases 1dB per stage for ( +25oC to -45oC)
Amplifier gain compensation is usually inserted either between amplifier stages or within various points in the receiver chain
• Temperature compensation options inculde:
PIN diode attenuators driven by a thermistor
MMIC attenuators
Variable gain amplifier
Balanced Amplifier
S11 = S22 = 0
BW 4:1
Ideal for cascading compact
If one stage opens, Pout drop 6dB
