BJT UHF Mixer · The subsequent steps will illustrate the procedure. NOTE: By convention for a...

Designing Single Ended UHF BJT Mixer

F.Kung Sep 2001 1

Designing A Single Ended UHF BJT Mixer Using the ADS Software

Objectives:

• A simple UHF Mixer operating at 430.0 MHz is designed. The RF signal at 430.0

MHz is down converted into IF frequency of 20.0 MHz.

• The mixer is targeted to have no attenuation (conversion gain of 0dB) and an

operating noise figure of less than 10dB.

• The design steps are divided into 5 parts. These are the DC biasing of the mixer

circuit, S-parameters measurement for RF and IF, input matching, output matching

and final design verification.

Background:

• The transistor chosen for the job is BFR92A which comes in SOT-23 package. The

maximum IC sustainable by the transistor is 30.0mA, with transition frequency fT =

5GHz.

• Since this is a large signal nonlinear circuit, substantial harmonics will be generated,

therefore the chosen simulation method is the Harmonic Balance Method.

• The transistor is biased in emitter degenerated common-emitter configuration.

• The mixer is driven by a RF source with 50Ohms source resistance, and LO (local

oscillator) source with 50Ohms source resistance and sustaining a load resistance of

50Ohms. The block diagram of the mixer is shown in Figure 1.

Figure 1 – Block diagram of the mixer circuit.

Step 1: DC biasing and S-parameters measurement

The raw circuit of the mixer is shown in Figure 2. LO signal is pumped into the emitter

of Q1 while RF signal is imposed on the base of Q1. This configuration improves

isolation between the LO, IF and RF signals. You will notice that each signal is

connected to different pin of the transistor. The LO signal is quite large, the BE junction

RF Source Input

Matching

Network

Core mixer

circuit

Local Oscillator

(LO)

Output

Matching

Network Load

Power supply and

decoupling


F.Kung Sep 2001 2

of Q1 serves to attenuate the LO power (See book by Razavi [1] or Lee [3]) This will

minimize radiation of the LO signal through the receive antenna. To further improve

isolation, the IF and RF port should have the following characteristics:

• At IF port, RF signal should be shunted, only allowing low frequency signal (IF) to

pass.

• At RF port, IF signal should be shunted, only allowing high frequency signal (RF) to

pass.

These characteristics can be simulated be inserting artificial elements at both ports. The

impedance of the element is a function of frequency. In ADS, this is implemented using

the equation based linear elements, which can be accessed from the “Eqn Based-Linear”

linear component palette.

For instance for ZIP1 at RF port, the impedance is equal to 1Ohm when signal frequency

is less than 100MHz and 1000Ohm at other frequencies. These artificial elements can be

realized using lumped elements after incorporating the matching networks at RF and IF

port. The subsequent steps will illustrate the procedure.

NOTE:By convention for a successful analysis of mixer:1. Set the RF input to PORT 1, IF output to PORT 2 and LO input to PORT 3 (by editing the NUM property).2. Set the signal with largest amplitude to Freq[1] to ensure convergence of the HB method.

Z_RF is to simulate short at IF and high impedance at RF.Z_IF is to simulate high impedance at IF and short at RF.A realistic value for short would be 1-5 Ohms while a realisticvalue for high impedance would be 500-2000 Ohms.

S_Param

SP1SweepPlan="SwpPlan1"

S-PARAMETERS

SweepPlanSwpPlan1

SweepPlan=UseSweepPlan=

Pt=430.0MHzPt=410.0MHzPt=20.0MHz

SWEEP PLAN

DC

DC1

DC

LLb

R=

L=220.0 nH

R

RbR=47 kOhm

VARVAR1

RF_pow=-20freq_RF=430 Mhz

freq_LO=410 Mhz

EqnVar

CCc2

C=10.0 pF

CCc3

C=330.0 pF

C

Cc1C=330.0 pF

RRLOR=50 Ohm

Z1P_EqnZ1P2

Z[1,1]=Z_IF

VARVAR2

Z_IF=if freq < 100MHz then 1000 else 1endifZ_RF=if freq < 100MHz then 1 else 1000 endif

EqnVar

Z1P_EqnZ1P1

Z[1,1]=Z_RF

Term

Term2

Z=50 OhmNum=2

TermTerm1

Z=50 Ohm

Num=1

V_DCSRC1Vdc=3.0 V

R

R2R=1 kOhm

R

ReR=330 Ohm

pb_phl_BFR92A_19921214

Q1

Figure 2 – The schematic of the raw mixer with no matching.

DC simulation is performed on the schematic and the transistor voltage and current is as

follows:

VC VE VB IC

1.82V 0.39V 1.14V 1.17mA

ZIP1

Low impedance at IF

and high impedance

at RF.


F.Kung Sep 2001 3

S-parameter Simulation

For mixer operation, we are only interested with S-parameters at 3 frequencies (IF =

20MHz, LO = 410 MHz and RF = 430 MHz), thus a sweep plan is used instead of

measuring the S-parameters at all frequencies. The Sweep Plan window can be accessed

from S-Parameters control as shown in Figure 3.

Figure 3 – Sweep Plan setting.

The result of S-parameters simulation is shown below:

freq20.00MHz410.0MHz430.0MHz

S(1,1)0.968 / -128.4900.876 / -22.6030.874 / -23.693

Z(1,1)1.000 - j24.115

77.551 - j224.54672.572 - j215.009

freq20.00MHz410.0MHz430.0MHz

S(2,2)0.817 / -1.036

0.961 / -177.3000.961 / -177.425

Z(2,2)493.913 - j44.025

0.999 - j1.1780.999 - j1.123

Table 1 – S-parameters for raw mixer circuit.

The input impedance at

IF and RF ports.

Assuming linear

operation.


F.Kung Sep 2001 4

Step 2: Harmonic Balance Simulation of Raw Mixer Circuit

In order to illustrate the effect of having proper impedance matching circuits at both RF

and IF ports, we perform a quick analysis of the raw mixer circuit. The schematic is

shown in Figure 4. L1 and C1 are arbitrarily added with the purpose of filtering out RF

signal from the IF port. Current probes are added as measuring power requires both

voltage and current information. If performing Harmonic Balance simulation for a circuit

with multi-tone sources, some precautions have to be taken to ensure convergence and

sufficient accuracy.

• The LO source, being larger in magnitude should be assigned to frequency [1] and

given a higher order (more harmonics are considered).

• The MaxOrder variable should follows the order of LO.


L

Lb

R=

L=220.0 nH

RRb

R=47 kOhm

HarmonicBalanceHB1

Order[2]=5

Order[1]=7Freq[2]=freq_RF

Freq[1]=freq_LOMaxOrder=7

HARMONIC BALANCE

DC

DC1

DC

VARVAR1

RF_pow=-20

freq_RF=430 Mhzfreq_LO=410 Mhz

EqnVar

P_1TonePrf

Freq=freq_RF

P=polar(dbmtow(RF_pow),0)

Z=50 OhmNum=1

CC1

C=47.0 pF

C

Cc3C=100.0 pF

I_Probe

ILoadL

L1

R=

L=100.0 nH

V_DCSRC1

Vdc=3.0 V

RR2

R=1 kOhm

RRL

R=50 Ohm

I_Probe

ISourceC

Cc1C=100.0 pF

CCc2

C=10.0 pF

P_1Tone

PLO

Freq=freq_LOP=polar(dbmtow(0),0)

Z=50 Ohm

Num=2

RRe

R=330 Ohm

pb_phl_BFR92A_19921214Q1

Figure 4 – Harmonic Balance simulation of raw mixer circuit.

Conversion Gain of Mixer

The conversion gain GC is defined as:

GC = PowerIF/PowerRF or GC = 10log10(PowerIF/PowerRF)

For this raw mixer schematic, it is (Refer to Appendix 2 for the data display)

GC = -18.866dB for RF_pow = -20dBm.

This source will

supply –20dBm

power to a matched

load, in this case

50Ω.

Built-in

function to

convert dBm to

Watt


F.Kung Sep 2001 5

Step 3: Performing Matching at RF and IF Ports

The input impedance at RF port is Zrf = 72.572 – j215.009Ω (From Table 1). We would

like to transform this to 50Ω to match to the RF source impedance. The schematic to

achieve this is shown in Figure 5.

This is the input impedance atRF frequency, from the stand-pointof RF source.

We would like to tranformthe impedance Z_in into50 Ohm, from the point ofview of the RF source afterthe L network.

C

Cm1

C=0.335 pF

VAR

VAR1

Z_in=72.572-j*215.009

EqnVar

L

Lm1

R=

L=68 nH

S_Param

SP1

Step=1.0 MHz

Stop=0.430 GHz

Start=0.430 GHz

S-PARAMETERS

Z1P_Eqn

Z1P1

Z[1,1]=Z_in

DC_Block

DC_Block1Term

Term1

Z=50 Ohm

Num=1

Figure 5 – Matching network design for RF port.

The input impedance at IF port is Zif = 493.913 – j44.025Ω (From Table 1). We would

like to transform this to 50Ω to match to the IF load impedance. The schematic to

achieve this is shown in Figure 6.

We would like to tranformthe load impedance intoconjugate of Z_if, from thepoint of view of the mixer IFoutput.Z_if = 493.913 - j*44.025

This is the load impedance atIF frequency, from the stand-pointof the mixer IF output

S_Param

SP1

Step=1.0 MHz

Stop=20 MHz

Start=20 MHz

S-PARAMETERS

L

Lm2

R=

L=1203 nH

C

Cm2

C=47 pF

R

RL

R=50 Ohm

DC_Block

DC_Block1Term

Term1

Z=50 Ohm

Num=1

Figure 6 – Matching network design for IF port.


F.Kung Sep 2001 6

Optimizing the IF Matching Network to Filter Out High Frequency Signal

The matching networks from Figure 6 is good enough for the IF port. However it is still

not sufficient for suppressing high frequency signals (note that the configuration of the

network is low pass). Cm2 = 47pF at 410MHz is only 8.26Ω. We would like to increase

Cm2 further to reduce this impedance (recall that the artificial device ZIP2 at RF is only

1Ω). This can be achieved by using a π network, with more degree of freedom we can

choose Cm2 to suit our purpose. The completed circuit is shown in Figure 7. Now at

410MHz, |XCm2| = 4.00Ω. This should be sufficient for bypassing RF signal, as the load

is 50Ω, so this impedance is 10 times smaller than load impedance.

We would like to tranformthe load impedance intoconjugate of Z_if, from thepoint of view of the mixer IFoutput.Z_if = 493.913 - j*44.025

This is the load impedance atIF frequency, from the stand-pointof the mixer IF output

S_Param

SP1

Step=1.0 MHz

Stop=20 MHzStart=20 MHz

S-PARAMETERS

C

Cm3

C=270.5 pF

L

Lm2

R=

L=800 nHC

Cm2

C=97 pFR

RL

R=50 Ohm

DC_Block

DC_Block1TermTerm1

Z=50 Ohm

Num=1

Figure 7 – Matching network design for IF port using π network.

NOTE

Note that in carrying out the impedance matching procedure, we are assuming the

transistor to be operating in a quasi-linear mode. It is nonlinear so as to produce the

mixing effect, yet the linearity is small enough so that the usual linear procedure and

concept of impedance can be applied. Usually this is a valid assumption.


F.Kung Sep 2001 7

Step 4: Complete Circuit Simulation and SSB Noise Analysis

After including the matching networks, the raw mixer circuit becomes as shown in Figure

8. At RF port, Lb together with Cbyp1 shunts the low frequency IF signal (at 20Mhz,

220nH inductance is considered small, only 27Ω). While at IF port, Cm2 serves to shunt

the RF signal.


Input matching network

Output matching network

VARVAR1

RF_pow=-20

freq_RF=430 Mhzfreq_LO=410 Mhz

EqnVar

CCc2

C=15.0 pF

CCdecC=1000.0 pF

Options

Options1

MaxWarnings=10GiveAllWarnings=yesI_RelTol=1e-6

V_RelTol=1e-6TopologyCheck=yesTemp=23.85

OPTIONS

HarmonicBalance

HB1

Other=OutVar="RF_pow"NoiseOutputPort=2

NoiseInputPort=1FreqForNoise=freq_RF-freq_LONLNoiseMode=yesOrder[2]=5

Order[1]=7Freq[2]=freq_RFFreq[1]=freq_LOMaxOrder=7

HARMONIC BALANCE

DCDC1

DC

R

RbR=47 kOhm

RR2R=1000 Ohm

P_1TonePrf

Freq=freq_RFP=polar(dbmtow(RF_pow),0)Z=50 Ohm

Num=1

TermTerm3

Z=50 Ohm

Num=2

P_1TonePLO

Freq=freq_LOP=polar(dbmtow(0),0)

Z=50 OhmNum=3

LLm1

R=

L=68.0 nH

I_ProbeISource

CCm3C=270.5 pF

LLm3

R=

L=800.0 nHCCm2C=97.0 pF

I_ProbeILoadC

Cc3C=330.0 pF

CCm1C=0.33 pF

C

Cc1C=330.0 pF

LLb

R=

L=220.0 nH

CCbyp1C=1000.0 pF

V_DCSRC1Vdc=3.0 V

RReR=330 Ohm

pb_phl_BFR92A_19921214Q1

Figure 8 – Complete mixer circuit.

We now set up the Harmonic Balance Simulation control. This time in addition to the

usual harmonic balance analysis, the nonlinear noise analysis is also activated. The

Option control is to set the operating temperature. The nonlinear noise window can be

accessed via the Harmonic Balance control as shown in Figure 9. The parameters for the

Noise[1] tab is as follows:

• Sweep Type : Point. We are analyzing spot noise here.

• Input frequency = RF frequency.

• Frequency: This is the frequency where the noise at IF port is measured. It is equal to

IF frequency or (RF frequency) – (LO frequency).

The Noise[2] and NoiseCons tabs are not used. When noise simulation is enabled, the

software will calculate the noise figure (NF) and equivalent noise temperature (TE) at

various ports of the circuit. These values will be included in the dataset after the

Harmonic Balance simulation is completed.

IF power

RF power


F.Kung Sep 2001 8

Figure 9 – Setting up nonlinear noise analysis through Noise[1] tab.

NOTE ON NOISE SIMULATION

1. Small-signal noise is used for circuits like amplifier. In this case the amplifier circuit

will be linearized at the d.c. bias point. Equivalent noise source will be impose on

elements such as PN junctions and resistors. System noise and noise figure are then

computed, either at one frequency (spot noise) or a band of frequency (wideband

noise).

2. Nonlinear noise is used for large signal circuits like power amplifier and mixer. It is

used with Harmonic Balance simulation where the noise must be computed at the

fundamental frequency, but also at the harmonics as well. Moreover the noise

voltage and current must be computed at various operating points of the steady

voltage and current since the circuit under analysis is a large signal circuit. Thus

nonlinear noise analysis requires much more computation power and memory than

just pure Harmonic Balance analysis.

This is the port where wide-band

noise is input (RF port).

This is the port where noise power is

retrieved (IF port).

To compute ‘spot’ noise.

The frequency where the noise will be

input to the circuit. In this case it is

the RF frequency for down-converter,

i.e. Noise_freq + LO_freq = RF_freq

Enable nonlinear noise simulation


F.Kung Sep 2001 9

3. Oscillation noise is used for computation of phase noise of oscillator. Again the noise

voltage and current need to be computed at various operating points under steady

state condition.

4. There are 2 methods for noise simulation, using the Noise[1] and Noise[2] tabs, and

using the NoiseCons tab. NoiseCons tab is used for several noise simulation, this

eliminates the need to change the values on the Noise[x] tab. It can be used for noise

sweeping calculation. Please refer to online help of ADS for more information.

Result

Upon running the simulation and using the data display as in Appendix to show the signal

spectrum, the conversion gain (for RF input power at –20dBm) is calculated as:

GC = -0592

This is a substantial improvement over the raw mixer circuit in Step 2, where the

conversion gain is only –18.866dB or 0.013. The voltage and current magnitude

spectrum is depicted in Figure 10. From the figure it is proven that output at IF port

consists mainly of a 20MHz component, the RF components are highly suppressed.

Furthermore the nonlinear noise analysis shows that the noise figure of the mixer is

roughly:

NFdB = 8.984 dB

Which is an acceptable value for single transistor mixer.


F.Kung Sep 2001 10

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

0.0000

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

f req, GHz

ILoad

.i

m3

m1freq=2.000E7HzVout=0.030 / -124.846

m2freq=4.700E8HzVout=2.016E-9 / 168.315

0.0 0.5 1.0 1.5 2.0

0.000

0.005

0.010

0.015

0.020

0.025

0.030

freq, GHz

Vout

m1

m2

Figure 10 – Magnitude of output voltage and current spectrum.

0 10 20 30 40 50 60 70 80 90 100

-40

-20

0

20

40

time, nsec

Vo

ut_

t, m

VIo

ut_

t, m

A

Figure 11A – Time domain steady state output voltage and current.


F.Kung Sep 2001 11

0 10 20 30 40 50 60 70 80 90 100

-250

-200

-150

-100

-50

0

50

100

150

200

250

time, nsec

Vin

_t, m

VIin

_t, m

A

Figure 11B – Time domain steady state input voltage and current.

Step 5: Gain Compression Test

By modifying the Harmonic Balance Simulation control, we could change the schematic

of Figure 8 into a gain compression test. This is done by sweeping the RF power level as

shown in Figure 12.

HarmonicBalance

HB1

Other=

Lin=10

Stop=10

Start=-30

SweepVar="RF_pow"

NoiseOutputPort=2

NoiseInputPort=1

FreqForNoise=freq_RF-freq_LO

NLNoiseMode=

Order[2]=5

Order[1]=7

Freq[2]=freq_RF

Freq[1]=freq_LO

MaxOrder=7

HARMONIC BALANCE

Figure 12 – Changing the HB Simulation control for gain compression test.


F.Kung Sep 2001 12

The result of gain compression test is shown in Figure 13. It is seen that 1dB gain

compression occurs roughly at RF input power level of –5dBm.

-30 -25 -20 -15 -10 -5 0 5 10

-40

-30

-20

-10

0

10

RF_pow

Pif_dbm

Pif_ext

Figure 13 – Gain Compression test.

References

• B. Razavi, “RF Microelectronics”, Prentice Hall, 1998.

• R. Ludwig, P. Bretchko, “RF circuit design – theory and application”, Prentice Hall,

2000.

• T.H. Lee, “The design of CMOS radio-frequency integrated circuits”, Cambridge

University Press, 1998.


F.Kung Sep 2001 13

Appendix 1 – Photograph of the constructed UHF mixer based on schematic of

Figure 8

Appendix 2 – Agilent ADS Data Display Used (ADS 2000)

Data Display for Conversion Gain and Nonlinear Noise Analysis:

Local Oscillator

Input

RF Input IF Output

To 3.0-3.3V D.C.

Source

1.57mm thick FR4 printed

circuit board

BNC to PCB

adapter

SMA to PCB

adapter


F.Kung Sep 2001 14

0.0 0.5 1.0 1.5 2.0

0

5

10

15

20

25

30

freq, GHz

Vo

ut,

mV

Use the mix( ) function to extract a certain frequency component.Since the simulation has two frequency sources, the frequency component indexes is two dimensional, i.e. m1,m2.For example mix(Vout, -1,1) extracts Vout at frequency 20MHz.The variables Mix(1) and Mix(2) is the frequency indexes. Usuallywe employ the list function to display the frequency components ofa voltage or current together with the indexes.

Eqn Vif = mix(Vout,-1,1)

Eqn Iif = mix(ILoad.i,-1,1)

Eqn Pif = 0.5*re(Vif*conj(Iif))

Eqn Pif_dbm = 10*log10(Pif) + 30

Eqn G_conv = Pif_dbm-RF_pow[0]

freq

20.00MHz

Pif_dbm

-20.592

G_conv

-0.592

Alternatively we could just write:Pif = mix(0.5*re(Vout*conj(ILoad.i),-1,1,Mix), Mix is variable forall frequency components, it is only needed when we want to extractan expression as in above.The conversion gain G_conv is defined as:

G_conv = 10*log(Pif/Prf)

freq0.0000 Hz20.00MHz40.00MHz60.00MHz350.0MHz370.0MHz390.0MHz410.0MHz430.0MHz450.0MHz470.0MHz490.0MHz780.0MHz800.0MHz820.0MHz840.0MHz860.0MHz880.0MHz900.0MHz1.190GHz1.210GHz1.230GHz1.250GHz1.270GHz1.290GHz1.310GHz1.330GHz1.620GHz1.640GHz1.660GHz1.680GHz1.700GHz

Vout0.000 / 0.000

0.030 / -124.8465.586E-5 / 115...1.242E-6 / 79....6.083E-9 / -16...4.881E-8 / -14...2.469E-7 / -15...7.107E-6 / 48....1.174E-6 / -13...6.112E-9 / 123...2.016E-9 / 168...2.372E-10 / -1...5.899E-9 / -10...5.177E-8 / -12...7.578E-7 / -14...1.668E-7 / 37....6.552E-9 / -13...1.754E-10 / -5...3.484E-11 / -1...3.924E-9 / 9.8962.127E-8 / 4.0761.508E-7 / -1.6...4.352E-8 / 178...3.191E-9 / 2.2014.725E-11 / 16...4.465E-12 / 18...2.797E-11 / 12...6.599E-9 / 143...3.168E-8 / 144...1.124E-8 / -40....1.154E-9 / 135...3.715E-11 / -4...

ILoad.i0.000 / 0.000

5.908E-4 / -12...1.117E-6 / 115...2.483E-8 / 79....1.217E-10 / -1...9.762E-10 / -1...4.939E-9 / -15...1.421E-7 / 48....2.348E-8 / -13...1.222E-10 / 12...4.033E-11 / 16...4.744E-12 / -1...1.180E-10 / -1...1.035E-9 / -12...1.516E-8 / -14...3.335E-9 / 37....1.310E-10 / -1...3.507E-12 / -5...6.967E-13 / -1...7.847E-11 / 9....4.255E-10 / 4....3.016E-9 / -1.6...8.704E-10 / 17...6.382E-11 / 2....9.450E-13 / 16...8.930E-14 / 18...5.595E-13 / 12...1.320E-10 / 14...6.335E-10 / 14...2.248E-10 / -4...2.307E-11 / 13...7.429E-13 / -4...

Mix(1)0

-1-2-343210

-1-2-343210

-1-2543210

-1-254321

Mix(2)0123

-3-2-101234

-2-101234

-2-1012345

-10123

noisefreq

20.00MHz

te(2)

2004.840

nf(2)

8.984

Noise Figure at IF output and the equivalent Noise temparature

The conversion gain. The index in RF_pow is arbitrary, as RF_powis a constant, it is the same for all frequencies.

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

0

100

200

300

400

500

600

freq, GHz

ILo

ad

.i,

uA

0.0 0.2 0.4 0.6 0.8 1.0

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

freq, GHz

ma

g(V

in)

0.0 0.2 0.4 0.6 0.8 1.0

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

freq, GHz

ma

g(I

So

urc

e.i

)

Check for Local Oscillator coupling to input port

Examining the time domain signals

Eqn Vout_t = ts(Vout)

Eqn Iout_t = ts(ILoad.i)

0 10 20 30 40 50 60 70 80 90 100

-40

-20

0

20

40

time, nsec

Vo

ut_

t, m

VIo

ut_

t, m

A

Eqn Vin_t = ts(Vin)

0 10 20 30 40 50 60 70 80 90 100

-250

-200

-150

-100

-50

0

50

100

150

200

250

time, nsec

Vin

_t,

mV

Iin

_t,

mA

Eqn Iin_t = ts(ISource.i)


F.Kung Sep 2001 15

Data Display for Gain Compresssion Test:

Eqn Vif = mix(Vout,-1,1)

Eqn Iif = mix(ILoad.i,-1,1)

Eqn Pif = 0.5*re(Vif*conj(Iif))

Eqn Pif_dbm = 10*log10(Pif) + 30

-30 -25 -20 -15 -10 -5 0 5 10

-40

-30

-20

-10

0

10

RF_pow

Pif_

db

mP

if_

ext

Equation to determine the IF output power

Steps to extrapolate the IF power

Eqn grad1 = (Pif_dbm[1] - Pif_dbm[0])/(RF_pow[1] - RF_pow[0])

Eqn C1 = Pif_dbm[0]

Eqn Pif_ext = grad1*( RF_pow - RF_pow[0]) + C1

Extrapolate IF power equation:


F.Kung Sep 2001 16

Appendix 3 – Measurement Results

A measurement is carried out to verify that the mixer does indeed function properly. The

Setup is shown in Figure A31. Key instruments used are an Agilent ESG series signal

generator, a normal 100MHz bandwidth bench top digital sampling oscilloscope (DSO),

power supply and an Agilent 89XX series Vector Signal Analyzer (VSA). The VSA is

only used as a spectrum analyzer in this instance, thus any low cost spectrum analyzer

will do.

Figure A31 – The measurement setup.

Figure A32 – Close-up view of the mixer.

Agilent ESG series

signal generator

Agilent 89XX

series VSA

100MHz digital

sampling

oscilloscope

(Tektronix)

Mixer & LO

Mixer

Battery to power

up mixer

From signal generator

(RF)

Variable

frequency

oscillator

(LO) Probe to

DSO (IF)

Power

supply

for LO


F.Kung Sep 2001 17

The settings for the various instruments are as follows:

LO:

RF source: frequency = 430.0MHz, Power = -20dBm into 50Ω load.

LO source: frequency ≈ 410 MHz , Power = -5.48dBm into 50Ω load.

Power supply for mixer: 3.0V.

Figure A33 – Time domain IF output when RF signal is activated.

Figure A34 – Time domain IF output when RF signal is deactivated.

The mixer can work properly for RF power level down to –50dBm, when IF output is

almost equivalent to the noise floor. It can work to a lower RF power level if the LO

power level is increase (say to 0dBm).

BJT UHF Mixer · The subsequent steps will illustrate the procedure. NOTE: By convention for a...

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