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