Quiz Draw a block diagram of a quadrature (I/Q) demodulator. Carrier Recovery cos(  o t) Splitter  /2) LPF Recovered Q Data: Q R (kT) Recovered I Data: I R (kT) Splitter S(t)

System Considerations: Receivers/Transmitters Increased integration of Broadband, High frequency RF components – understanding of the performance and specification limitations of these devices is critical to system designers. Sensitivity/Minimum Detectable Signal Transmitter Power Gain/Bandwidth characteristics Intermodulation (linearity) Filter characteristics Frequency conversion techniques Active/Passive Nonlinear/commutating Balanced/unbalanced Image/Spurious products Propagation Issues Path loss/Fading Diversity Frequency Re-use/Co-channel Interference

System Considerations: Receivers/Transmitters (cont) Modulation/Demodulation Types and techniques Frequency Translation Spectrum Shaping Waveform Synthesis PLL Frequency Synthesis FDMA TDMA CDMA Direct Sequence/Frequency Hopping Digital Aspects A/D, D/A, Nyquist E b /N 0 BER Symbol Alphabets Decision Based modulation/demodulation schemes Coding/FEC

System Considerations: Receivers Front End Issues T/R antenna switching Diplexers Diversity Switching Preselector/Image rejection Low Noise/ High Gain in first Stage (LNR) Sensitivity power Level S(watts):

Image Reject Mixers Local Oscillator cos(  LO t) Splitter  /2) LPF Splitter S(t)  /2)  v o (t) v A (t) v B (t) High Side Injection:  S =  LO -  IF

Local Oscillator cos(  LO t) Splitter  /2) LPF Splitter S(t)  /2)  v o (t) v A (t) v B (t)

Local Oscillator cos(  LO t) Splitter  /2) LPF Splitter S(t)  /2)  v o (t) v A (t) v B (t) High Side Injection:  IM =  LO +  IF

Local Oscillator cos(  LO t) Splitter  /2) LPF Splitter S(t)  /2)  v o (t) v A (t) v B (t)

Phase Noise PcPc frequencyf0f0 ff f

Reciprocal Mixing Example Local oscillator phase noise is characterized with S c (f) = 60 dBc/hz at 50 kHz displacement from center frequency. The Local Oscillator puts out P c = +10 dBm, and the IF Bandwidth is 10 kHz. What is the effective LO power available for reciprocal mixing of a strong signal displaced 50 kHz from the desired channel? The phase noise power available to mix with the interfering channel will occupy a bandwidth equal to the IF bandwidth, located 50 kHz away from the LO. S c (50 kHz) = 60 dBc/hz (1/S c = ) ;  f = 10 kHz and P c = 10 mw, therefore the effective LO power for reciprocal mixing with the interfering signal is P r = (10 mw) (10 kHz)(10 -6 ) = 0.1 mW

Quiz What is the root cause, and what frequency combinations cause third order intermodulation interference? Nonlinear gain causes on-channel interference when strong signals are spaced at  f and 2  f from the desired channel.

P N,i P N,o P SF P s,i P s,o P d,o P d,i P IP,i P IP,o Response to Signal Response to Interference SNR IMDR P o (dBm) P i (dBm) “Spurious Free” rd Order Intercept Point Intermodulation Characteristics

Example An amplifier has a gain of 22 dB and a 3 rd order output intercept point of 27 dBm. Assume the effective noise input power is P N,i = -130 dBm. Determine Spurious Free Range P N,i + G = P N,o = P d,o = 3(P SF + G) – 2P IP,o P SF = (P N,i + 2P IP,o -2G)/3 = (– 130 dBm + 54 dB – 44 dB)/3 = – 40 dBm Determine IMDR for an input signal level of -80 dBm and SNR = 15 dB. P s,i + G – SNR = P d,o = 3(P d,i + G) – 2P IP,o P d,i = (P s,i – SNR + 2P IP,o -2G)/3 = (– 80 dBm – 15 dB + 54 dB – 44 dB)/3 = – 28.3 dBm IMDR = – 28.3dBm – (– 80 dBm) = 51.7 dB

P SF S/N IMDR P s,i P d,i P d,o P N,i P N,o P s,o P IP,o