（转）rfic求职面经

Does Mash 1-1-1 have a high requirement on PFD ?  
----Yes. More strict on PFD linearity due to 8 modes output of Mash, compared to 4 modes output of Single-loop.
How to decide the input bits of SDM?
-----fref/synthesizer’s frequency resolution
How to decide the period of MASH 1-1-1 output sequence ?
----divider out clock cycle
Draw the SDM output PSD of noise and signal on a coordinate axis with
MATLAB?
频综里VCO电感如何在面积与性能上优化的
1.    centre tapped differential L
2.    More center area, higher Q.
3.    Moderate Width
4.    Circle shape better for Q
PLL的spur如何抑止，
----For reference spur, smaller LBW(not Icp),higher fref,smaller PFD delay,smaller Icp mismatch, I leakage
----For fractional spur, higher linearity of PFD+CP. Good isolation.smaller LBW
环路带宽如何选取对phasenoise的影响
----In band PN (CP/ref/div)  and out band PN (VCO) trade-off.
DNW MOSFET的优缺点，
----Advantage: 1. Isolation. 2. Can connect NMOS S and B
Disadvantage: 1. More area 2.Extra ground or no effect
CML结构 的缺陷
----Static power.  Differential input needed. Large area. Need current bias.
comparator的preamplifier增益带宽如何设定
----?
LNA做输入匹配的原因
----1.Reduce return loss. 2. Increase power gain. 3. Decrease NF. 4. Maintain SAW filter performance (if any)
降低one-of-f对Phase noise 的贡献
----VCO?  1.Symmetric.  2.Filtering methods. 3.Small ISF
电感modeling与PGS，
------Pattern ground shielding. Poly or metal.To avoid inductor substrate loss and the shielding eddy current. Better for Q. Bad for self resonate freq.
Lna与mixer之间若插入 filter，对NF影响？
------Which filter? Isn’t LNA load a bandpass filter?
VCO中varactor的最大最小电容之比，
----Cox/Cdep
尾电流源噪声滤波技术
---- Low pole at current source gate. Using by pass switch if fast start up needed. Second harmonic LC at virtual ground.
Maybe just a resistor is better than any.
divider的相位噪声曲线
---- 1/f noise and thermal noise
频综双模分频的缺陷，
----Timing margin. Limited divider ratio. A little higher power
comparator的滞回现象
---- ?