Low Noise Amplifier

DSB/SC-AM Modulation (Review)

Frequency Shift Property (Review)

Frequency Spectrum of DSB/SC-AM Signal (Review)

If the Receiver Uses a Different Frequency to Demodulate

(Keep by using with LPF)

Use an LNA Circuit to Reduce Noise

(11/20) (11/27)

(12/4)

Design of a Low Noise Amplifier

1. Transistor Biasing2. Add L1 (Ls) and Lg3. Add Ls4. Adjust Lg5. Generate gate bias voltage6. Add M27. Design the output resonant network8. Reduce the quality of output tank!

Design of a Low Noise Amplifier

• Source Resistance (RS) is 50 Ω

• Assume a bias current of 1 mA• Assumed: gm/ID=20 mS/mA

Determine M1

Initial assumptions:1. VDS1=0.3 V2. VSB=0 V (DC)3. gm/ID=20 mS/mA4. ID=1 mA

gm/ID Calculation

Device Simulation

Add L1& Lg

Impedance Measurement

Our initial L1 and Lg does not produce a perfect match!

Increase Ls to Increase Real Impedance

(Increase Ls (or L1) to compensateFor CGD)

(Ls=270 pH)

(Ls=398 pH)

(The resonant frequency is still off!)

Adjust Lg

(fix at 3.5 GHz )(Reduce Lg to increase the resonant freq)

Generate the Gate Voltage

The resistor RB and CBisolate the signal pathfrom the noise of IB and MB.

Generate VGS of M1 (449.8 mV)

Insulate the DC

Find the width of MB

Determine RB

RB must be much larger than RP, the parallel equivalent resistanceOf RS. Otherwise, RB will load the input match network!

Input Bias Network!

Lg=14.85 nH, Ls=398 pH

After adding the bias MBBefore adding the bias MB

Determine M2

(Choose M2 to beIdentical to M1, for simplicity)

Also connect the gate ofM2 to VDD.

Determine the Output Impedance

Use large L to provide DC bias and open at 3.5 GHz.Use an artificially large C to provide DC isolation and a short at 3.5 GHz.Use the port to calculate the S22 and output impedance.

Output Admittance

Goal: to cancel the imaginary admittance with an inductor!An effective output capacitance of 135 fFAn effective output resistance of 1/1.107mS=900 OhmsSince we know fo, and Ceff, we can calculate Leff: 15.3 nH

Adding Output Capacitance

• A 15.3 nH inductor is too large to implement on silicon.

• We will add a 1 pF capacitor in parallel to reduce the required inductance to 1.82 nH

Schematic

(A port is used to calculate the output impedance)

903~1/1.107 mS

Comparison of Smith Chart

After adding the bias MB After the output loadThe input resonant frequencyalso shifted.

Location of S11 @ 3.5 GHz!

Input Resonant Frequency Shifted to 3.15 GHz

We probably have to reduce Lg.

Real and Imaginary Part of Output Impedance

Adjust Lg to Move the Resonant Frequency to 3. 5GHz

S11 Using Lg of 10 nH

Input S11

Reflection coefficient larger than 1!

May have to adjust reducethe quality factor of the output tank!

Adjust Output Resistance

RL of 900 Ω

Transient Simulation

Trasient Simulation

Vout=1.225-1.1745=50.5 mVVin=441.637-439.96=1.67 mVAv=30.23, 29.60 dB

Misc.

Determine Parameters Using Matlab

DC Bias Simulation

Purpose: Verify gm/ID DC parameters through simulation.

Design of a Low Noise Amplifier

• Source Resistance (RS) is 50 Ω

• Assume a bias current of 1 mA• Assumed: gm/ID=20 mS/mA