L3

Question 1

Main properties of chipless RFID tags

Answer 1

• need to maximize power absorption
• use a rectifier circuit to convert incoming RF signal from reader into DC
• reader keeps on transmitting a continuous-wave signal to interrogate the tag
• tag reflects signal back after modulation
• employ amplitude or phase shift keying

Question 2

name modulation techniques used in chipless RFID systems and draw schematic (L3 4,5)

Answer 2

• Amplitude shift keying (ASK)
• On-off keying (OOK)
• Phase shift keying (PSK)

Question 3

draw simplified circuit of how ASK and PSK can be implemented (L3 6,7)

Answer 3

write on paper

Question 4

basic concept of backscatter modulation

Answer 4

• based on switching between two different impedance states using two complex impedances

Question 5

draw basic backscatter modulation scenario (L3 9)

Answer 5

write on paper

Question 6

write radar cross section equation and explain main idea (L3 10)

Answer 6

• the main idea is to have the two states of the signal as separated as possible, lambda1 and lambda2 are very different. The best way is to have capacitive and inductive impedances.

Question 7

How can BER be maximized?

Answer 7

by maximizing the power absorption vy the tag

Question 8

draw L-section matching networks (L3 15)

Answer 8

write on paper

Question 9

draw series-parallel and parallel-parallel ASK and PSK configurations (L3 16) include antenna and rectifier (17)

Answer 9

write on paper

Question 10

analyse operation of series-parallel ASK modulator (L3 18-20)

Answer 10

• when switch is open, tag resembles a purely-resistive circuit. Complete absorption of power from antenna by rectifier occurs
• when switch is closed, tag resembles a purely-reactive circuit

Question 11

Define BER and equation in backscatter ASK modulation (L3 22)

Answer 11

• BER is energy per bit over noise level

Question 12

Main properties of PSK backscatter modulation

Answer 12

• information represented via phase difference
• phase angle must be maximized maintaining constant power magnitude
• realized by introducing complex impedance and complex conjugate right after antenna

Question 13

draw basic PSK backscatter modulator diagram (L3 27)

Answer 13

write on paper

Question 14

draw series-series PSK modulator (L3 29) and main properties

Answer 14

• modulator is assumed to operate beyond resonance
• magnitude of reflection coefficient must be constant otherwise amplitude modulation occurs

Question 15

impedance representation of the two states of series series PSK modulator (L3 32)

Answer 15

write on paper

Question 16

alternative to PSK backscatter modulation and reason to be used

Answer 16

• can be difficult to achieve exact 180° modulation angle in PSK backscatter
• pseudo-PSK backscatter