MULTI-STAGE AMPLIFIERS

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MULTI-STAGE AMPLIFIERS: LARGE-SIGNAL DESIGN:

MULTI-STAGE AMPLIFIERS: LARGE-SIGNAL DESIGN By Tabassum unnisa rvce , bangalore

Contents:

Contents Introduction Analysis Multi-stage amplifier Third order intercept point power Dynamic range consideration Wide dynamic range Multi-stage amplifier Problem solution

INTRODUCTION:

INTRODUCTION A power amplifier (PA) is a circuit for converting DC input power into a significant amount of RF/microwave output power. In a high power amplifier, each stage should be designed for operation at maximum power ,such that, maximum power transfer condition is met. Most important parameters that defines an RF Power Amplifier are: Output power 1-db gain compression point Dynamic range Third order intercept point power Efficiency

1-db gain compression point:

1-db gain compression point The point at which the power gain of the transistor, due to non- linearities , is reduced by 1 dB from it’s small signal linear power gain value. G 1dB =G 0dB -1dB G 1dB =P 1dB /P in,1dB P 1dB ( dBm ) =P in,1dB ( dBm ) + G 1dB (dB) DR = P 1dB -P 0,mds (dB)

Analysis of MULTI-STAGE AMPLIFIERS:

Analysis of MULTI-STAGE AMPLIFIERS M1 M3 M2 Mn 50 Ω Stage 1 Stage 2 Stage n N-stage FET amplifier

PowerPoint Presentation:

Maximum power transfer conditions

Third order intercept point power:

Third order intercept point power 1/P TOI =1/P TOI,n +1/( G Pn P TOI,n-1 )+-----+ 1/( G Pn G Pn-1 G P2 P TOI,1 ) Where, Gp is power gain. If all stages are identical, i.e., Gpk = Gp , k=1,2,…n P TOI,k =P, k=1,2,…n Geometric series identity

PowerPoint Presentation:

As Third order intercept point is a power amplifier figure of merit

Wide dynamic range Multi-stage amplifier design:

Wide dynamic range Multi-stage amplifier design For n-stage amplifier, DR=P 1dB,cas ( dBm )-(P 0,mds ) cas ( dBm ) a)From (P 0,mds ) cas ≥(P 0,mds ) 1 ,we can conclude that first stage sets the lower limit and ideally, (P 0,mds ) cas =(P 0,mds ) 1 b) From P 1dB,cas ≤ P 1dB,n ,we can observe that the upper limit is determined by 1-dB gain gain compression point of the last stage and ideally, P 1dB,cas = P 1dB,n

Wide dynamic range contd..:

Wide dynamic range contd.. Thus , the maximum dynamic range or the best estimate of the dynamic range, DR max = P 1dB,n ( dBm )-(P 0,mds ) 1 ( dBm )

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