Experiment 3 - High Frequency Amplifiers.
S. Levy, H. Moalem, D. Ackerman and Dr. H. Matzner.
Febuary, 2009.
Contents
1 Objectives
2
2 Prelab Exercise
2
3 Background Theory
2
3.1 The amplifier which we will use - Mini-Circuits amplifier ERA−3+ 3
3.2
3.3
General Definitions . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating Frequency Range . . . . . . . . . . . . . . . . . . . . .
3
3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
S21 -Gain . . . . . . . . . . . . . . . . . . . . . . .
S11 and S22 − Input and Output SWR . . . . . .
S12 −Reverse Isolation . . . . . . . . . . . . . . .
Gain Flatness . . . . . . . . . . . . . . . . . . . .
Output Power at 1 dB Compression . . . . . . .
Dynamic Range of an Amplifier . . . . . . . . . .
Intermodulation Products . . . . . . . . . . . . .
Noise Figure (NF) . . . . . . . . . . . . . . . . .
3.11.1 The Importance of NF . . . . . . . . . . .
3.11.2 Noise Figure Measurement - Gain Method
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4 Experiment Procedure
4.1
4.2
4.3
4.4
10
Required Equipment . . . . . . . . . . . . . . . . . . . . . . . . .
S Parameters - Simulation and Measurement. . . . . . . . . . . .
4.2.1 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.2 Measurement . . . . . . . . . . . . . . . . . . . . . . . . .
1 dB Compression Point - Simulation and Measurement. . . . . .
4.3.1 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3.2 Measurement . . . . . . . . . . . . . . . . . . . . . . . . .
Third Order Intermodulation Products Point - Simulation and
Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4.1 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . .
1
10
10
10
11
15
15
16
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17
4.5
4.6
4.7
4.8
4.4.2 Measurement . . . . . . . . . . . . . . . .
Absolute Noise Power Measurement . . . . . . .
4.5.1 Measurement . . . . . . . . . . . . . . . .
Noise Figure of Cascade Amplifiers . . . . . . . .
4.6.1 Measurement . . . . . . . . . . . . . . . .
Dynamic Range and Minimum Detectable Signal
Final Report . . . . . . . . . . . . . . . . . . . .
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5 Appendix A - Data Sheet of the ERA-3+ Amplifier
1
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18
19
19
20
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21
22
22
Objectives
Upon completion of this study, the student will become familiar with the following topics:
1. Basic operation of the amplifier.
2. 1 dB compression point.
3. Third order intermodulation products.
4. Noise figure of an amplifier.
2
Prelab Exercise
1. Define the terms: ’dynamic range’, ’minimum detectable signal’, ’1 dB compression point’ and ’third order intercept point’.
2. Explain how you intend to measure the noise figure of a preamplifier using
a spectrum analyzer, 50 Ω termination and another preamplifier.
3. Calculate the Minimum Detectable Signal (MDS) for B = 100 kHz, N F =
2.65 dB, G = 22 dB and SN R = 5 dB, according to the equation:
M DS [dBm ] = −174 + 10 log B + N F [dB] + G [dB] + SN R [dB]
3
Background Theory
The components which we have discussed so far in previous experiments have
been primarily linear and passive, but any useful RF or microwave system, such
as a receiver, will require some nonlinear and active components. Such devices
include amplifiers, diodes and mixers, which can be used for detection, mixing,
amplification and frequency conversion.
An RF power amplifier is a type of electronic amplifier used to convert a
low-power radio-frequency signal into a larger signal of significant power.
2
3.1
The amplifier which we will use - Mini-Circuits amplifier ERA − 3+
An industrial preamplifier which we will discuss later is shown in Figure 1.
C1
Input capacitor
R1
Amplifier
ERA-3
R2
C2
Output capacitor
C3
Figure 1 - A preamplifier.
3.2
General Definitions
Amplifier are classified by several attributes, namely:
* Operating Frequency Range.
* Gain.
* Gain Flatness.
* Output Power at 1 dB Compression.
* Input and Output SWR.
* Dynamic Range.
* Noise Figure.
* Intercept point.
3.3
Operating Frequency Range
The operating frequency range is the range of frequencies over which the amplifier will meet the specification parameters. The amplifier may perform beyond
this frequency range (without any commitment).
3
S12
S22
Amplifier
S11
S21
Figure 1: Figure 2 - Scattering parameters of an amplifier.
3.4
S21 -Gain
Small signal gain is defined as the ratio of the power measured at the output of
an amplifier to the power provided to the input port. It is usually expressed in
decibels and is typically measured across the operating frequency range.
G(dB) = 10 log |S21 |
3.5
(1)
S11 and S22 − Input and Output SWR
Most RF and microwave amplifiers are designed as close as possible to 50Ω
impedance. However, this is not always possible, especially when attempting
to simultaneously achieve a good noise figure. The SWR of an amplifier is
the measure of an amplifier’s actual impedance, Z, with respect to the desired
impedance (Z0 ), which is in most cases 50 Ω. In general, SWR of a single stage
amplifier can be no greater than 2:1. When cascading such amplifier, the SWR
could be about 2.5:1.
3.6
S12 −Reverse Isolation
Reverse isolation defines the isolation between input and output of an amplifier.
Typically reverse isolation is twice the gain.
3.7
Gain Flatness
Gain flatness describes the variation in an amplifier’s gain over the operating
frequency range (see Figure 3) at any fixed defined temperature within the
operating temperature range.
The gain flatness of an amplifier is measured by viewing the gain variation
and determining the difference between the minimum gain and the maximum
4
gain recorded over the operation frequency range.
Gain (max)
Gain(dB)
Gain variation (dB)
Gain (min)
Frequency Range
Figure 3 - Gain flatness.
3.8
Output Power at 1 dB Compression
The 1dB output compression point of an amplifier is defined as the output power
level at which the gain degrades from the small signal gain by 1 dB. All active
components have a linear dynamic range. This is the range over which the
output power varies linearly with respect to the input power. As the output
power increases to near its maximum, the device will begin to saturate. The
point at which the saturation effects are 1 dB from linear is defined as the 1 dB
compression point (see Figure 4). Because of the nonlinear relation between the
input and output power at 1 dB compression, the following equation holds:
RF output power
Pout1dB = Pin1dB + GLinear − 1dB
1 dB
compression
Linear
Region
RFInput power
Figure 4 - 1dB compression point.
5
(2)
3.9
Dynamic Range of an Amplifier
Suppose that we have an amplifier which fulfill:
Pout = 10Pin
for a specified range of input power. When the input power increases, the
amplifier is no longer a linear component and the output begins to saturate.
When the input power decreases to zero, there is still an output power from internal and external noise. This level of power caused by the amplifier’s internal
noise is often called noise floor level of the component. Typical values can range
from -60 dBm to -100 dBm over the bandwidth of the system, with lower values
being obtainable with cooled components. A quantitative measure of the onset
of saturation is called the ’1 dB compression point’, which is defined as the
input power for which the output is 1 dB below the power of an ideal amplifier.
If the input power is excessive, the amplifier can be destroyed. A typical graph
of the behavior of this amplifier is shown in Figure 5.
output power(dBm)
Ideal amolifier
burn
out point
1dBcompression
point
small signal
gain
dynamic
range
SNR
Noise level
Input power (dBm)
Figure 5 - Dynamic range.
3.10
Intermodulation Products
The non-linear behavior of a component causes undesired output harmonics. In
general, the voltage transfer function of a non-linear device is:
2
3
vout = a0 + a1 vin + a2 vin
+ a3 vin
+ ...
(3)
For amplifier, the desired response is the linear. Higher order responses are
undesired.
6
If the input of a component consists of a single frequency (or tone), for
example vin = cos f1 t, then the output voltage will consist of all harmonics mf1 .
where m is called the order of the harmonics. For an amplifier we need only
order = 1, and the presence of higher harmonics is called harmonic distortion. If
an amplifier had a bandwidth of an octave or more, the second-order distortion
product of a low-frequency signal could be in the passband of the amplifier.
If the input to the system consist of two relatively closely, spaced frequencies
(two-tones), say vin = cos f1 t + cos f2 t, the output spectrum will consist of
all harmonics of the form mf1 + nf2 ,where m and n are positive or negative
2
integers. The order of a given product is then defined as |m| + |n| . The vin
term
will produce harmonics at the frequencies 2f1 ,2f2 , f1 − f2 and f1 + f2 ,which are
all second order products. These frequencies can be filtered out, except the case
of a broadband amplifier.
3
The vin
term will lead to third-order products, such as 3f1 , 3f2 , 2f1 +f2 ,which
can be filtered, but 2f1 − f2 and 2f2 − f1 cannot be filtered even for a narrowband system. These products, which result from mixing two input signals, are
called the ’intermodulation distortion’. Hence these two products will set the
3
dynamic range or bandwidth of the amplifier. Higher powers than vin
can also
contribute to the intermodulation distortion, but generally these contributions
are not dominant.
These spurious signals are characterized with respect to the input signal by
means of a theoretical tool called ’the intercept point’. This point is defined
as the point where the linear curve of the input Vs. output power of the fundamental signal would intersect with the linear curve of the spurious signal if
saturation effects would not limit the output levels of these signals (see Figure
6). Since it is known that the second order spurious products (f2 ± f1 ) have a
slope of 2:1 with respect to the fundamental input power, the value of the spurs
can be estimated if the input power (Pin ) and the output second order intercept
point are known. The relationship is as follows:
A measure of the second or third-order intermodulation distortion is given
by the intercept points. An example of a graph with interception points is given
in Figure 6, for the frequencies f1 or f2 . The amplifier will work well for a input
power which is below the third interception point.
7
output power(dBm)
Third order
intercept
small
signal
gain
spurious
free
dynamic
range
1 dB
compression
point
second order
product
Noise level
Input
power(dBm)
Figure 6 - IP3 point.
3.11
Noise Figure (NF)
Noise figure represents the degradation in signal to noise ratio as the signal
passes through a device or a system. F is the noise factor of the system and is
calculated as:
Sin /Nin
(4)
F =
Sout /Nout
Where Sin /Nin and Sout /Nout are the input and output signal-to-noise ratios. Since all devices add a finite amount of noise to the signal, F is always
greater than 1.
Alternatively, noise figure may be defined in terms of dB units:
N F = 10 log10 F = Sin /Nin [dB] − Sout /Nout [dB]
3.11.1
(5)
The Importance of NF
The increased in low noise preamplifier and other RF components usage leads
to a need for reliable and inexpensive noise figure measurement systems. If no
specialized equipment is available, the problem of measuring NF can be solved
using modern spectrum analyzer as a noise power meter.
Why noise figure is important Noise figure is a key performance parameter
in many RF systems. A low noise figure provides improved signal to noise
ratio for analog receivers, and reduces bit error rate in digital receivers. As a
parameter in a communications link budget, a lower receiver noise figure allows
smaller antennas or lower transmitter power for the same system performance.
8
3.11.2
Noise Figure Measurement - Gain Method
This method is based on direct noise measurement and is applied using the
measurement setting, as shown in Figure 7, and pre-determining the gain of the
DUT.
Assuming Sin = Nin we get:
Ftotal =
Sin /Nin
Nout
kT BG1 G2 + Nadded
Pmeasured
=
=
=
Sout /Nout
Sout
kT BG1 G2
kT BG1 G2
(6)
Where FT otal - total noise factor of the DUT and the preamplifier.
Pmeasured - noise power in Watts, displayed on the spectrum analyzer.
B - noise bandwidth.
G1 and G2 - linear gains of the DUT and
£ preamplifier ¤respectively.
k - Boltzmann constant (1.38 · 10−23 Joul · Kelvin−1 ).
T - temperature in Kelvin (room temp = 27 ◦ C = 300 K).
The noise factor of two cascading amplifiers is:
Ftotal = F1 +
F2 − 1
G1
(7)
Where F1 and F2 - noise factors of the DUT and preamplifier respectively.
If the NF of the preamplifier and gain of the DUT are known, one can
calculate the noise factor of the DUT by:
F1 = Ftotal −
F2 − 1
G1
preamplifier
(8)
Spectrum analyzer
DUT
50 Ohm
termination
G1
NF=?
G2
NF=known
Figure 7 - Equipment setting for gain method.
This measurement set-up is valid, when implementing the following rules:
• The DUT is matched with the characteristic impedance, Z0 .
• In order to minimize the effect of the second amplifier, we have to choose
low noise amplifier, (minimum noise figure) while the gain of the DUT is
sufficient large (see equation 7).
• The spectrum analyzer has the capability of measuring noise (the ability
to correct the bandwidth of the measurement and take into account the
random nature of the noise).
9
• Maximum accuracy could be achieved when Pmeasured ≥ DAN L + 10 dB
(DANL - ’Displayed Average Noise Level’ of the spectrum analyzer).
The advantages of this method are:
• Low price and measurement simplicity - only absolute power value reading on spectrum analyzer, and minimum measuring set. It is possible to
perform quick noise figure measurement in a wide frequency range, thanks
to the sweeping capability of the spectrum analyzer.
• Output instability or other interference can be easily seen.
The major disadvantage of this method are:
• The spectrum analyzer has the capability of measuring accurately only
very low noise signal (DAN L < −120dBm).
• The gain of the DUT should be at least 10 dB for reasonable accuracy.
• This method requires that the gain of the DUT is known already. Also,
the accuracy of Noise Figure measured depends directly on the accuracy
of the measured Gain.
4
4.1
Experiment Procedure
Required Equipment
1. Network analyzer.
2. RF power amplifier Mini-Circuit ERA − 3 + .
3. DC power supply.
4. Two signal generators.
5. Attenuator.
4.2
4.2.1
S Parameters - Simulation and Measurement.
Simulation
1. Simulate the preamplifier Mini-circuit ERA − 3+, according to Figure 1.
10
S-PARAMETERS
S_Param
SP1
Start=10 MHz
Stop=1 GHz
Step=1.0 MHz
Term
Term1
Num=1
Z=50 Ohm
va_mc_ZFL-1000LN_19930601
Amp1
Term
Term2
Num=2
Z=50 Ohm
Figure 1 - S-parameter simulation.
2. Simulate all the S parameters (S11 , S22 , S21 and S12 ) of the preamplifier
as a function of frequency. Frequency range 50M Hz − 1GHz. Save the data
on magnetic media.
4.2.2
Measurement
For the old network analyzers 3. Set the power level of the network
analyzer to -10 dBm by pressing POWER, Level, -10 dBm and set the
frequency range to 50 M Hz − 1 GHz
4. Connect a coaxial cable between port 1 and port 2 of the network analyzer,
as shown in Figure 2 (If the network analyzer can’t reach to a power level of
−10 dBm, than add an appropriate attenuator, as shown in Figure 5). Preform
a transmission calibration.
11
RF
IN
RF
out
Coaxial cable
Figure 2 - Transmission calibration, without attenuator.
5. Disconnect the coaxial cable from port 1 and connect the amplifier between
port 1 and the coaxial cable, as shown in Figure 3. Connect the amplifier to a
DC power supply of 12V. Measure S21 and S12 . Save the data on magnetic
media.
Pay attention to the polarity and to the input power level,
otherwise you may blow up the amplifier!
Important:
Network Analyzer HP8714
RF
O UT
RF
IN
ERA-3+
Figure 3 - Transmission measurement, without attenuator.
6. Disconnect the amplifier and the coaxial cable from the network analyzer
and preform a reflection calibration.
7. Connect the IN port of the amplifier to port 1 of the network analyzer
and the OUT port of the amplifier to a 50 Ω termination, as shown in Figure 4.
12
Measure S11 and S22 . Save the data on magnetic media.
N etw ork A nalyzer H P 8714
RF
OUT
RF
IN
E R A -3+
50Ω
Load
Figure 4 - Reflection measurement, without attenuator.
Compare the measured result to the simulated result. Compare the measured
SWR input, SWR output and gain to the data sheet (see appendix A).
For the new network analyzer 3. Set the power level of the network
analyzer to -5 dBm by pressing Sweep Setup, Power, -5 dBm and set the
frequency range to 50 M Hz − 1 GHz.
4. Connect a 6 dB attenuator to port 1 of the network analyzer and a coaxial
cable between the attenuator and port 2 of the network analyzer, as shown in
Figure 5. Preform a transmission calibration.
13
Network Analyzer HP-8714
RF OUT
RF IN
10.7 MHz
BPF
Attenuator
Figure 5 - Transmission calibration, with attenuator.
5. Disconnect the coaxial cable from the attenuator and connect the amplifier
between the attenuator and the coaxial cable, as shown in Figure 6. Connect
the amplifier to a DC power supply of 12V. Measure S21 and S12 . Save the
data on magnetic media.
Pay attention to the polarity and to the input power level,
otherwise you may blow up the amplifier!
Important:
Network Analyzer HP8714
RF
OUT
Attenuator
RF
IN
ERA-3+
Figure 6 - Transmission measurement, with attenuator.
14
6. Disconnect the amplifier and the coaxial cable from the network analyzer
and preform reflection calibration.
7. Connect the IN port of the amplifier to the attenuator and the attenuator connect to port 1 of the network analyzer. Connect the OUT port of the
amplifier to a 50 Ω termination, as shown in Figure 7.
Measure S11 and S22 . Save the data on magnetic media.
N etw ork A nalyzer H P 8714
RF
OUT
RF
IN
Attenuator
E R A -3+
50Ω
Load
Figure 7 - Reflection measurement, without attenuator.
Compare the measured result to the simulated result. Compare the measured
SWR input, SWR output and gain to the data sheet (see appendix A).
4.3
4.3.1
1 dB Compression Point - Simulation and Measurement.
Simulation
1. Simulate the preamplifier Mini-circuit ERA − 3+, according to Figure 8.
15
HARMONIC BALANCE
SweepPlan
SwpPlan1
Start=-30 Stop=10.0 Step=1.0 Lin=
UseSweepPlan=
SweepPlan=
Reverse=no
HarmonicBalance
HB1
Freq[1]=1.0 GHz
Order[1]=5
SweepVar="Pin"
SweepPlan="SwpPlan1"
Pout
P_1Tone
PORT1
Num=1
Z=50 Ohm
P=dbmtow(Pin)
Freq=RFfreq Hz
GAIN COMPRESSION
SWEEP PLAN
va_mc_ZFL-1000LN_19930601
Amp1
Term
Term2
Num=2
Z=50 Ohm
XDB
HB2
Freq[1]=RFfreq
Order[1]=5
GC_XdB=1
GC_InputPort=1
GC_OutputPort=2
GC_InputFreq=1.0 GHz
GC_OutputFreq=1.0 GHz
GC_InputPowerTol=1e-3
GC_OutputPowerTol=1e-3
GC_MaxInputPower=100
Var
Eqn
VAR
VAR1
RFfreq=1GHz
Pin=-5
Figure 8 - 1dB compression point simulation.
2. Draw the graph of the idealized linear power gain and the graph of the
actual power curve.
Do so by constructing the equations:
Linear=Gain[1]+XDB1,HB1,HB1,HB,Pin
Gain=dBm(XDB1,HB1,HB1,HB,Vout[1])-XDB1.HB1.HB.Pin
Where ’Linear’ is the idealized linear power gain and ’Gain’ is the graph of
the actual power curve.
3. Find the exact 1 dB point at the data display window by placing two
markers, one marker on the linear curve and the other on the actual curve and
turn on delta marker mode. What is the input power which result in a difference
of 1dB between the markers? Save the data.
4.3.2
Measurement
For the old network analyzers 4. Set up the network analyzer by pressing
BEGIN, Amplifier and Transmission. Choose power sweep instead of frequency sweep by pressing SWEEP, Power Sweep. Choose Continuous Wave
for only one frequency of 1GHz by pressing FREQ, CW, 1GHz. Set the power
sweep range to its maximum by pressing POWER, PwrSweepRange, -6 to
Max (dBm), Prior Menu, Start, -6 dBm, Stop, 20 dBm.
5. Connect a 20dB attenuator to the network analyzer with a coaxial cable, as shown in Figure 5. Preform a transmission calibration and connect the
amplifier between the attenuator and the coaxial cable, as shown in Figure 6.
Connect the amplifier to a DC power supply of 12V.
For the new network analyzer 4. Set up the network analyzer by pressing
16
Meas, S21. Choose power sweep instead of frequency sweep by pressing Sweep
Setup, Sweep Type, Power Sweep. Choose Continuous Wave for only one
frequency of 1GHz by pressing Power, CW Freq, 1GHz. Set the power sweep
range by pressing Start, -5 dBm, Stop, 10 dBm.
5. Connect a 10 dB attenuator to the network analyzer with a coaxial cable,
as shown in Figure 5. Preform a transmission calibration and then connect
the amplifier between the attenuator to the coax cable, as shown in Figure 6.
Connect the amplifier to a DC power supply of 12 V .
Important : Pay attention to the polarity and the input power level, otherwise you could blow up the amplifier!
6. A graph of the P out/P in versus P in is displayed. Place a marker on
the graph and find the P in which result in a 1 dB drop in the P out/P in value.
Save the data on magnetic media.
According to the data sheet, the 1dB compression point at 1GHz is 12.53dBm.
Compare your result to the theoretical.
4.4
Third Order Intermodulation Products Point - Simulation and Measurement.
In this part of the experiment you will simulate and measure the IP3 of a
preamplifier.
4.4.1
Simulation
1. Simulate the preamplifier according to Figure 9.
HARMONIC BALANCE
HarmonicBalance
HB1
Freq[1]=1 GHz
Freq[2]=999 MHz
Order[1]=3
Order[2]=3
Attenuator
P_1Tone ATTEN1
PORT2 Loss=3 dB
Num=2
VSWR=1
Z=50 Ohm
P=dbmtow(-15)
Freq=1 GHz
BPF_Elliptic
Attenuator
BPF1
ATTEN2
Fcenter=1 GHz Loss=6 dB
BWpass=100 MHzVSWR=1
Ripple=0.01 dB
BWstop=200 MHz
Astop=40 dB
Attenuator
P_1Tone ATTEN3
PORT1 Loss=3 dB
Num=1
VSWR=1
Z=50 Ohm
P=dbmtow(-15)
Freq=999 MHz
BPF_Elliptic
Attenuator
BPF2
ATTEN4
Fcenter=999 MHz Loss=6 dB
BWpass=100 MHzVSWR=1
Ripple=0.01 dB
BWstop=200 MHz
Astop=40 dB
Pout
PwrSplit2
PWR1
S21=0.707
S31=0.707
Attenuator
ATTEN5
Loss=3 dB
VSWR=1
Figure 9 - IP3 simulation.
17
Attenuator
va_mc_ZFL-1000LN_19930601
ATTEN6
Amp1
Loss=3 dB
VSWR=1
Term
Term3
Num=3
Z=50 Ohm
2. Drew a graph of P out [dBm] as a function of frequency.
Double click on the graph, go to ’Trace Options’ and change the selected type
from ’Auto’ to ’Spectral’. Double click on the graph, go to ’Plot Options’ and
set the frequency range to 990MHz-1010MHz. Save the data on magnetic
media.
A typical view of intermodulation products is shown in Figure 10.
Amplitude
IM,dBc=A
2F!-F2
F2
F1
2F2-F1
Frequency
Figure 10 - Intermodulation products.
3. Calculated the IP 3,using the formula IP 3 = P + A/2, where P is the
output power of the fundamental signal (f1 or f2 ) .
4. Change the power of the input generators to -20dBm and drew the same
graph as in paragraph 2. Save the data on magnetic media.
Verify that the IP3 point has no major changes.
4.4.2
Measurement
5. Connect the system as indicated in Figure 11.
Sig.
Gen.1
3dBpad
BPF
6dB
pad
Sig.
Gen.1
3dBpad
BPF
3dBpad
DUT
Comb
iner
3dBpad
6dB
pad
Figure 11 - System configuration for an IP3 measurement..
18
Spectrum
Analyzer
6. Set Sig Gen.1 to frequency 1000M Hz and amplitude −15dBm.
Set Sig Gen2. to frequency 999M Hz and amplitude −15dBm.
Watch the fundamental and third order products on the spectrum analyzer
(set the spectrum to an average of 20). Save the data on magnetic media.
7. Fill in Table-1:
Signal [dBm] 1st order freq.&Amp.
3rd order freq. &Amp.
IP3 [dBm]
-15
-20
Table-1
8. Compare your simulated result to your measured result of the IP3 and to
the theoretical one.
4.5
Absolute Noise Power Measurement
In this part of the experiment you will measure the noise floor of a spectrum
analyzer.
4.5.1
Measurement
1. Connect a 50 Ω termination to the input of the spectrum analyzer, as shown
in Figure 12.
Spectrum Analyzer Agilent-ESA
50Ω
Load
Figure 12 - Measuring the noise floor of a spectrum analyzer.
2. Set the spectrum analyzer to center frequency of 100 M Hz, span of
1 kHz, average on and a reference level of −100 dBm.
3. Measure the noise floor of the spectrum analyzer by using marker noise:
For the new spectrum analyzers Press Marker, More, Function, Marker
Noise.
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For the old spectrum analyzers Press MKR FCTN, MK NOISE, ON.
Save the data on magnetic media.
4.6
Noise Figure of Cascade Amplifiers
In this part of the experiment you will calculate the noise figure of one amplifier
by measuring the noise figure of cascade amplifiers.
4.6.1
Measurement
1. Set the power level of the network analyzer to −10 dBm and the frequency
range to 50 M Hz − 1 GHz. Connect a coaxial cable between port 1 and port
2 of the network analyzer, as shown in Figure 2 (If the network analyzer can’t
reach to a power level of −10 dBm, than add an appropriate attenuator, as
shown in Figure 5). Preform a transmission calibration.
2. Connect two series amplifiers to the network analyzer (don’t forget the
attenuator, if needed), as shown in Figure 13.
Important:
Pay attention to the polarity and to the input power level,
otherwise you may blow up the amplifier!
Network Analyzer HP8714
RF
OUT
ERA-3+
RF
IN
ERA-3+
Figure 13 - Measuring the gain of a cascade of two amplifiers.
3. Measure the linear gain (S11 ) of two cascade amplifiers (G1 G2 ) at 100 M Hz.
Save the data on magnetic media.
4. Connect two amplifiers in series, as shown in Figure 14.
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Spectrum Analyzer Agilent-ESA
ERA-3+
ERA-3+
50Ω
Load
Figure 14 - Measuring noise figure of cascade amplifiers.
5. 2. Set the spectrum analyzer to center frequency of 100 M Hz, span of
100 kHz.
Measure the noise power (in Watts) by the noise marker.
6. Calculate the noise figure of the first amplifier.
7. Compare your measured result of the NF to the theoretical one.
4.7
Dynamic Range and Minimum Detectable Signal
1. Connect the system as indicated in Figure 14.
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Spectrum Analyzer ESA-E
Signal Generator Agilent 8648
515.000,00 MHz
ERA-3+
ZFL-1000LN
Figure 14 - Dynamic range and minimum detectable signal measurement.
2. Set the spectrum analyzer to center frequency 500 M Hz, span 100 kHz,
attenuation 0 dB and average on.
Set the signal generator to 500 M Hz and an amplitude which is comparable
to SNR of 5 dB.
Verify that the calculated MDS (question 3 from the ’Prelab Exercise’) is
within 3 dB of the measured MDS.
3. Calculate the dynamic range (DR) as:
DR [dB] = Pout_1dB [dB] − M DS [dB]
4.8
Final Report
1. Attach and explain all the graphs and simulation results.
2. Draw a graph of the output third order intercept point for the preamplifier
mini-circuit ERA − 3+ (see Figure 6 of the ’Background Theory’ part).
5
Appendix A - Data Sheet of the ERA-3+ Amplifier
Gain at 50 M Hz - 22.97 dB.
Gain at 1 GHz - 21.13 dB.
1 dB compression point at 50 M Hz - 12.72 dBm.
1 dB compression point at 1 GHz - 12.53 dBm.
IP3 at 50 M Hz - 26.87 dBm.
IP3 at 1 GHz - 27.45 dBm.
NF at 100 M Hz - 2.7 dBm.
NF at 1 GHz - 2.6 dBm.
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