Amplifiers Amplifier Parameters 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 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 -10 Power Gain: Gain = Pout/Pin Gain (dB) = Pout - Pin (dBm) Gain changes with output power level. 1 dB compression point Saturation gain Pout (dBm) Linear gain -30 -20 -10 0 10 Pin (dBm)

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. Efficiency:  = Pout/(Pdc in + Pin) Power added efficiency Bandwidth: BW = (fH-fL)/fM fM = (fH-fL)/2

Intercept Points 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 an amplifier can be written as Vo = a1Vi + a2Vi2 + a3Vi3 + ... where Vo and Vi are the output and input voltage of the amplifier; a1, a2, etc. are the coefficients The second order term( a2Vi2 creates second order intermodulation The third order intercept point (a3Vi3 creates third order intermodulation

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 Ripple components in RF out (-60dBc) Intermodulation product:

Types of Microwave Semiconductor Amplifiers Power Amplifiers LNA

(1) Select transistor [S-and Noise parameters) 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

Le gain à 1.64 GHz est de 16.61 dB 25 -25 25 -25 S21 S11 (dB) 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