I'm attempting to create a sensitive, precise mixed signal system (more than 24bit) compose of a backplane and stacked modules on 2.54mm headers.It is multi-channel and channel's modules are well separated with independent supplies of their own.
The only common module is the DSP, therefore all separate GNDs of all modules will meet at a single point is the DSP's supply GND.

My questions are :

Please take a look and see if there is any problem with my wiring ( quick draft attached below ), both in DC and low-freq noise ( shared impedances in GND return paths ) and HF, spiked noise ( digital and analog return flows ) ?

Is there any advice/caution regarding making a system on backplane ? The 2.54mm hdrs are good enough for 50-100MHz signal ? Any caution making connection through these tiny pins, especially with GND involved ? Should I treat the BCKPLN as a board of wires and traces only, or make use of it's copper planes for some further benefits ?


Here is a quick draft of system wiring :

quick draft of system wiring


1 Answer 1


If you trash your sensors, by having PowerSupply trash use the sensor-to-ground path --- ohmic or displacement currents(capacitive) --- then you'll have a 10 bit system.

How bad can this be?

Suppose your SwitchingRegulator has 100pF of capacitance between Line and Output, with 200 volt/200nanosecond edges across that 100pF. The current needing a return path --- and all possible return paths will be explored thru all your sensors --- is

I = C * dV/dT = 100pF * 200v/200nS = 1e-10 * 1e+9 = 0.1 amp

And the driving force is that 200 volts.

Do you wanna bet you can achieve 24 bits, with 0.1 amp exploring all possible stray parasitic paths?


Suppose one of the sensors is a strain gauge, 200 ohm resistance, glued onto a machine axle with 10pF sensor-shaft/gnd capacitance. What trash-floor can you expect?


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