ELEC 477/677
Topics in Wireless System Design
Spring 2006
Review Topics for Exam #3
The following is a list of topics that could appear in one form or another on the exam. Not all of
these topics will be covered, and it is possible that an exam problem could cover a detail not
specifically listed here. However, this list has been made as comprehensive as possible. You
should be familiar with the topics on the previous review sheets in addition to those listed below.
Receiver system design considerations
- front end design of typical superheterodyne receiver
- homodyne (direct conversion) receiver
- advantages of frequency translation (heterodyning) as opposed to TRF architecture
o allows optimization of narrow filter at IF instead of moving the passband of the
filter
o amplifiers do not all have to operate at the same frequency (aids stability)
o tuning accomplished by moving the frequency of a single oscillator; in general,
filters passbands do not have to be tuned
Mixers
- primary purpose is to provide frequency translation (frequency shifting)
- two inputs: RF signal and LO signal
- second-order outputs are signals at sum and difference frequencies (of RF and LO)
- image response
- IF and LO range selection
- diode ring mixer (doubly balanced; provides isolation of input/output ports)
- image rejection mixer
- phase detector
Nonlinear operation of mixers and amplifiers (intermodulation distortion, or IMD)
- representation of output signal as Taylor series
- 1st-order products are linear outputs
- 2nd-order, 3rd-order, etc. are intermodulation products
- dB level of third-order products increases three times as fast as that of first-order products
as input power increases (output power of desired signal is directly proportional to input
power, but IM3 products are proportional to input power cubed)
- third-order intercept point (TOI or IP3 or P3), referred to input or output
- compression point (or compression level)
- dynamic range
o blocking dynamic range: BDR 1 dB (dB)  Pin,1 dB  MDS in , where Pin,1 dB is the
input power level at the 1-dB compression point; MDSin is the minimum
detectable input signal
o “two-tone” third-order, or spurious-free, dynamic range:
2
2
SFDR(dB)  IP3in  MDS in   IP3out  PNOISE  , where IP3in is the third-order
3
3
input intercept point; PNOISE is output noise level
o MDSin = kToBF usually, but could be higher if min. SNR is specified
Noise in receiver systems
- sources of noise
o radiated noise (picked up by antenna or receiver circuitry)
o conducted noise (picked up by power and/or other cables)
o internally-generated noise (thermal, shot, and flicker)
- usually only internally-generated noise can be controlled by designer
- signal-to-noise ratio (SNR)
o output SNR is less than (worse than) input SNR
P
GPSi
PSi
o SNRo  So 

 SNRi
PNo GPNi  PNG PNi  PNG G
where PSo = output signal power, PSi = input signal power, PNo = output noise
power, PNi = input noise power, PNG = internally-generated noise power, and
G = gain of the stage
- standard noise factor
o standard input noise power: PNi  kTo B ,
where k = Boltzmann’s constant (1.38 × 10-23 J/K), To = standard room
temperature (290 K), and B = bandwidth of stage or system (narrowest)
PN
o F  1
, or
GkTo B
o PN  F  1GkTo B
o noise factor is always > 1
- standard noise figure (NF): NF  10 log F 
- noise floor of amplifier
o output: PNOISE  PNo  kTo BGF
-
-
o output noise power referred to input: PNo  kTo BF (equivalent to input noise of
ideal noiseless amplifier that produces same output noise as real amplifier)
overall standard noise factor
FN  1
F  1 F3  1


o Ftot  F1  2
G1
G1G2
G1G2  G N 1
o each noise factor in the equation is a standard noise factor
o the first one or two stages in a receiver are the most critical determiners of the
overall system noise figure
o for passive (no transistors or diodes), lossy, impedance-matched stages: G  1 L
and F  L
minimum detectable signal (MDSin)
o defined as the input noise floor, given by PNo plus min. SNR (in dB)
o min. acceptable SNR is often specified as 0 dB
o related to noise factor by MDSWatts   kTo BF  SNR
o related to noise figure by MDS(dBW)  10 log kTo B   NF  SNR(dB) , or
 kT B 
MDS(dBm)  10 log  o   NF  SNR(dB)  174 dBm  NF  SNR(dB)
 0.001 
Basic purpose and operation of the spectrum analyzer
Basic mixer circuit measurements
Diplexer circuits
- splits signals between two paths, depending on frequency
- purpose is to provide a constant-impedance termination for a circuit, regardless of
frequency
- design of simple diplexer (combination of simple LPF and simple HPF)
Relevant coursework and textbook sections:
HW:
Labs:
Textbook:
Lecture notes:
Supp. reading:
#7-#8
#8-#9
Secs. 9.11, 10.11, and 10.13
“System Noise Performance”
“Mixers and Mixer Performance”