A NEW METHOD TO STABILIZE HIGH FREQUENCY HIGH GAIN CMOS LNA RF Communications Systems-on-chip Primavera 2007 Pierpaolo Passarelli

A new method to stabilize high gain high frequency CMOS LNA2 21/06/2007 Presentation Introduction Theoretical analysis about the new idea Characteristics and calculation of the parameters of the device Simulation and results of the modified circuit respect to the basic circuit Differences with the paper results Conclusions

A new method to stabilize high gain high frequency CMOS LNA3 21/06/2007 Introduction RF front-end: LNA set the overall Noise Figure of the system Actual challenge: push CMOS LNA to work at higher frequency bands for newer generation wireless systems Current issue: very low stability at very high frequency

A new method to stabilize high gain high frequency CMOS LNA4 21/06/2007 The new topology The usual cascode architecture provide high gain, minimum noise figure, isolation between input and output that increase the stability LNA become less stable when the operation frequency approaches to f T of the device To increase the stability a small inductor is used in the gate of the cascode device

A new method to stabilize high gain high frequency CMOS LNA5 21/06/2007 Analysis of the new design The stability factor is defined as: Where ∆ = S 11 S 22 –S 12 S 21 Decreasing S 12 (reverse gain) with all the other S parameters quite constant => K increase L Z along with inherent capacitors of the device provide a low impedance path at desired band for signal that comes from output to ground, preventing it to leak back to the input This LC network provide a zero in reverse transmission path to reduce the effects of output signal at the input of LNA

A new method to stabilize high gain high frequency CMOS LNA6 21/06/2007 Analysis of the new design Usually when gain increase stability decrease L Z can be ignored on the output impedance (C gd low => high impedance) Since the gain of the amplifier equals to the transconductance multiplied by the output impedance => L Z doesn’t affect the gain of the amplifier

A new method to stabilize high gain high frequency CMOS LNA7 21/06/2007 Characteristics of the device Technology: 0.18um Contest: CMOS LNA for WLAN at 5.2GHz Power supply: 1.8V I DLNA : 9mA

A new method to stabilize high gain high frequency CMOS LNA8 21/06/2007 Calculations of the component size Optimum device width: Bias voltage: Degenerated source inductance: Noise Figure: Gate inductance: Drain inductance and capacitor:

A new method to stabilize high gain high frequency CMOS LNA9 21/06/2007 Complete Circuit

A new method to stabilize high gain high frequency CMOS LNA10 21/06/2007 Simulation Results Without L Z With L Z = 446.8pH NF (dB) S 11 (db) S 22 (dB) S 12 (db) S 21 (db) K IP3 (dBm)

A new method to stabilize high gain high frequency CMOS LNA11 21/06/2007 Simulation Results

A new method to stabilize high gain high frequency CMOS LNA12 21/06/2007 Differences with the paper Probably duty to the strong differences in the output network of the circuit the values are completely different About the performance we can focalize on S 12 and K:  In the paper 20 dB decrease in S 12 will result in ten times increase in stability factor  In this case 15db decrease in S 12 will result in 5.5 times increase in stability factor

A new method to stabilize high gain high frequency CMOS LNA13 21/06/2007 Conclusions In conjunction with improvements in CMOS technology, this new circuit technique will permit the design of high gain, stable CMOS LNAs for high frequency cellular application This method can be used to stabilize every kind of CMOS amplifier

A new method to stabilize high gain high frequency CMOS LNA14 21/06/2007 Thank you! Any question?