DREXEL UNIVERSITY

CAD Experiment V: Microwave Amplifier

Objective: To design and simulate performance of a low noise amplifier

Jinadu,Olaniyi3/16/2015

CAD Experiment V: Microwave Amplifier

Objective: To design and simulate performance of a low noise amplifier

A. Simulations Set-up A:1. Consider the BJT transistor that you have used in CAD Lab #1 (i.e., Agilent

HBFP0420 SOT-343) where typical S and noise parameters for bias of VCE= 8 V and Ic=36 mA at 850 MHz are available from the manufacturer data sheet. Create the DC biasing circuit for operation over 800- 1100MHz.

2. Simulate stability factor, k, and stability measure, B1 and print over frequency of 50 - 3000 MHz in steps of 100 MHz and identify range for unconditionally stable.

3. Simulate and plot input and output stability circles from 800 to 1100 MHz in steps of 100 MHz.

B. Simulations Set-up B:1. Find whether the transistor is conditionally stable at 950 MHz and find the

input and output impedance (reflection coefficient) for highest available gain and calculate this gain. Calculate available power gain (GA), Unilateral measure U, transducer gain (GT and GTU), and stable gain (Gms).

2. Realize the input and output matching networks using microstrip lines on a FR4 substrate. Compare realization of single stub matching against a quarter wave transformer as a function of frequency. (Use open circuited stubs.)

3. Simulate and plot input and output VSWR as a function of frequency from 500 to 1300 MHz.

C. Simulations Set-up C:1. Use noise parameters and plot noise figure in steps of 0.25 dB as a function

of source impedance at 950 MHz.2. Plot available power gain (GA) in steps of 1 dB. Select a source reflection

coefficient for optimum compromise on available gain and noise figure.3. Design input and output matching networks and simulate for VSWR.

Questions:1) Discuss how to achieve VSWR≤ 1.8 over frequency of 900 to 1000 MHz? How

would you modify the design approach?2) Is the LNA stable? If not stable, how to overcome the stability problem?3) How to satisfy all the LNA performance requirements? What are the

compromises?4) Problems 12.7, 12.9, 13.2, 14.11 from on reserve textbook by Radmanesh.

Please use the Matlab program provided by TA, Yaaqoub Malallah, to solve for problems 12.7 and 13.2.

SIMULATIONS SET-UP A:The DC-Biasing circuit with Vce = 8V; Ic = 36mA

For the circuit to be unconditionally stable K (StabFact) > 1 & B (StabMeasure) > 0

The unconditionally stable criteria are only met when the frequency is less than 90 MHz and when the frequency is beyond 5.083 GHz.

The input and output stability circles are given as;

Since the |S11| < 1 and |S22| < 1, the shaded region is the stable region.

SIMULATION SET-UP B:The reflection coefficients at 950 MHz are given as;

The stability circle at 950 MHz is given as;

The shaded region is the stable region

STABLE REGION

STABLE REGION

From the Smith chart above, Гs = 0 and ГL = 0.44 < 9.50. Using the MATLAB code below;

FORMULAR MATLAB CODE

GammaL = 0.44*(cosd(9.5) +sind(9.5)*1i);

GammaIn = S11 + ((S12*S21*GammaL)/(1 - (S22*GammaL)));GammaIn_mag = abs(GammaIn);GammaIn_phase = atand((imag(GammaIn))/(real(GammaIn)));

VSWR_In = (1 + GammaIn_mag)/(1 - GammaIn_mag);

GammaS = 0;

GammaOut = S22 + ((S12*S21*GammaS)/(1 - (S11*GammaS)));GammaOut_mag = abs(GammaOut);GammaOut_phase = atand((imag(GammaOut))/(real(GammaOut)));

VSWR_Out = (1 + GammaOut_mag)/(1 - GammaOut_mag);

|Гin| = 0.765 < 1; |Гout| = 0.727 < 1. The amplifier is conditionally stable.

Available StableGain ,G=¿S21∨¿

¿S12∨¿=21.5230.019

=1132.79=30.54 dB¿¿

Available PowerGain ,GA=1−¿ Г s∨¿2

¿1−S11Г s∨¿2 ¿S21∨¿2 1¿1−ГOUT∨¿2=29.9235dB ¿

¿¿¿

PowerGain ,GP=1−¿Г L∨¿2

¿1−S22Г L∨¿2 ¿S21∨¿2 1¿1−Г ¿∨¿2=32.69dB ¿

¿¿¿

TransducerGain ,GT=1−¿ Г s∨¿2

¿1−Г¿ Г s∨¿2¿ S21∨¿21−¿ Г L∨¿2

¿1−S22 Г L∨¿2=28.8651dB ¿¿¿¿

¿

Unilateral TransducerGain ,GTU=1−¿ Г s∨¿2

¿1−S11Гs∨¿2¿ S21∨¿21−¿ Г L∨¿2

¿1−S22Г L∨¿2=28.8651dB ¿¿¿¿

¿

The GT = GTU because Гs = 0

Input and Output Networks can be used to stabilize an amplifier at a certain frequency;

The matching design using a transmission line and a single stub can be seen in Smith Chart (1) above.

The design was realized using FR4 substrates below;Transmission line length = 127.10

Single Stub length (OC Shunt) = 43.20

The stability measure and factor, VSWR and transcendence gain is given as;

STABILITY MEASURE AND FACTOR

VSWR TRANSDUCER GAIN

ANALYSIS:As the plots above will show, stability has been achieved at 950 MHz since K = 1.198 > 1 and B = 0.471 > 0 and the gain of 27 dB can be measure which is close to the 28 dB calculated. The VSWRout is 2.540 which is close to the designed 2.

The matching design using a transmission line and a single stub can be seen in Smith Chart (2) below.

The design was realized using FR4 substrates below;Transmission line 1 length = 85.320

Transmission line 2 impedance = 31.623 Ω

The stability measure and factor, VSWR and transcendence gain is given as;

STABILITY MEASURE AND FACTOR

VSWR TRANSDUCER GAIN

ANALYSIS:As the plots above will show, stability has been achieved at 950 MHz since K = 1.344 > 1 and B = 0.405 > 0 and the gain of 27.753 dB can be measure which is close to the 28 dB calculated. The VSWRout is 2.019 which is close to the designed 2.

The use of quarter-wave matching is a better option because it offers better accuracy design wise and also produces a higher gain.

SIMULATION SET-UP C:

The Гopt is 0.034 < -157.6790 and since this is close to the origin, and close to the 30 dB gain circle, Гs can be selected as zero and the matching network of set-up B can be used here too.

HOMEWORK & QUESTIONS:1. Discuss how to achieve VSWR≤ 1.8 over frequency of 900 to 1000 MHz? How

would you modify the design approach?

When conjugate matching is used to match the amplifier at the input and output, VSWR = 1 so in order to reduce VSWR less than 1.8, the matching circuits have to designed with Гs close to Гin

* while ГL has to be close to Гout

*

2. Is the LNA stable? If not stable, how to overcome the stability problem?

The LNA is stable but if it was not stable we will have to design the LNA choosing Гs and ГL so that |Гin| < 1 and |Гout| < 1.

3. How to satisfy all the LNA performance requirements? What are the compromises?

As the name may suggest, the two major factors for a LNA is a low noise figure and a high gain. The issue is, the higher the gain, the higher the noise and the lower the gain, the lower the noise so one will have to compromise between the amount of noise figure and the maximum achievable gain.VSWR will also be factor when it comes to LNA design but Гs is going to be used to select the noise figure and gain so that does not allow much flexibility when it comes to VSWRin and for VSWRout it is always optimal for ГL = Гout

*.

4. Problems 12.7, 12.9, 13.2, 14.11 from on reserve textbook by Radmanesh. Please use the Matlab program provided by TA, Yaaqoub Malallah, to solve for problems 12.7 and 13.2.

Given the S-parameters above, the centers and radii of the stability circles can be calculated using;

CL = 1.1734 < 142.30; CS = 1.4867 < 75.630

RL = 0.426; RS = 0.8953

Using the MATLAB code;GT = 9.333 dBGP = 9.7713 dBGA = 9.4175 dB