There are 2 options for bulk connection in the MOS transisor:
1. connect it to Vss for NMOS and Vdd for PMOS
2. always connect it to the source of the transistor
What I've seen, in analog (low-freq) circuits, bulk is usually connected to the ground (or Vdd), but in RF circuits - to the source (in TSMC 0.18u RF transistor even does not have a bulk terminal).
Can someone clarify when which option is reasonable?
I have checked TSMC's documentation: RF transistor has 3 terminals, bulk is always connected to source. Does it mean that the bulk of such NMOS transistor is layed out in a seperate p-Well?? Or using guard ring around it NMOS transistor will prevent substrate coupling?
I am still in the black.
I am using TSMC 0.18um, PDK 1.3B. It provides RF transistors with 4 terminals (G, D, S, P).
Should I connect Bulk of RF transistor to GND (NMOS) or to Vdd (PMOS) (Vbs ≠0)?
Though question.. if the process allows it I would use the active well (e.g. well connected to any potential) everytime I need speed, as you minimize the Vth shift and you can eventually get rid of Cbs and Cbd (think about connecting the well to a common mode voltage)..
You can find there a lot of interesting things.
I recommand you:
Substrate Noise Coupling Analysis in Mixed-Signal ICs
Parasitic Coupling in RF Circuits: A Real-Life Experience
Do We Have RF Performance Degradation Due to Substrate Noise?
Substrate Effects in Smart-Power ICs
Read the first one, and you will find a lot of answers.