Please kindly help me think (predict) a few questions regarding transceiver (GSM/WCDMA) that interviewer could ask.
This position is an Application Engineer so they won't ask IC process question.
Could you please proivde must-know questions with transceiver ?
Such like "what is DC-Offset" , "What is (dis)advantage of Zero-IF architecture"...
Thanks for your help.
DC offset is the mean amplitude of a waveform. DC offset is usually undesirable. For example, in audio processing, a sound that has DC offset will not be at its loudest possible volume when normalized (because the offset consumes headroom), and this problem can possibly extend to the mix as a whole, since a sound with DC offset and a sound without DC offset will have DC offset when mixed. [ref. wikipedia]. You can simply eliminate it with a high-pass filter.
The advantages of a Zero-IF (Direct-Conversion) architecture are;
1)relatively simple, 2)highest integration potential, 3)no image problem
The disadvantage may be
1) DC offset
modulation ,and demodulation schemes , some about system design like NF of cascaded block
the blockers performance , enhancement of sensitivity
matching networks
PA loading
IP3 and NF of cascaded blocks, different Transceivers toplologies like superheterodyne, low IF and zero-IF, image rejection including filters (real and complex),blocker mask ,pulse mask,i think also some modulation schemes, AGC,...............
The best question/answer showing the experience of the interviewed guy is the following one:
Which is the relation between the phase noise of the local oscillator (LO) of any zero IF transciever and the SNR of the output signal in the absence of the IQ baseband modulator ? The transciever has an internal PLL with a multiplication factor set on 62.5 and LO = 40Mhz.
I would be asking que's about forward and reverse bias power supplies, advantages and effecencies, for todays power hungry world, and of coarse the software designed radioes and new band split requirements.
Which is the impact of of parallel routing of the IQ signals with ground shield available versus non parallel routing or I routed on different layer than Q ?
Disadvantage of zero dc offset IF is that it is sensitive to noise and small interference in the circuit and cause the system to saturate quickly.
So any small interference from LO/supply/etc cause the receiver goes to saturation .
Mehdi
Added after 2 hours 8 minutes:
there might be some question about noise figure / gain /AGC dynamic range calculation as well
Mehdi