Low Noise Amplifier. DSB/SC-AM Modulation (Review)
Post on 23-Dec-2015
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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
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