Can a circuit at 70MHz work stable on a 2 layer board?

[bluerainbow]

thanks.

 

[cyr]

What kind of circuit?

The short answer is yes (I've run pretty complicated things much faster on 2 layer homemade boards), but of course it depends...

If the circuit is so simple that you can route all the signals on one layer and keep the other one for a ground plane you can build pretty much anything with 2 layers.

 

[bluerainbow]

There are so many wires in the circuit.I can not provide a ground plane,and what is the fastest speed that a 2 layer board can do.
Thanks.

 

[rfmw]

I suppose you're talking about digital circuit, right? Remember to keep all high-speed connections as short as possible with as much ground-plane on the other side as possible.

But as mentioned before, it depends on many factors, that it will work as desired...

I've successfully ran 4 (72-macrocell) CPLDs at 60 MHz clock, but the PCB has somewhat good groundplane on the oposite side of the signal-plane...

Perhaps, your knowledge is your only limitation

 

[flatulent]

Even if you succeed with good signal integrity so that the circuit functions, you will very likely not pass the government EMI tests and not be able to sell the product.

 

[bluerainbow]

Thanks for all your advice.
to rfmw:
I want to enlarge my knowledge ,but I do not know where to find PCB board design resources and what knowledge I need.Would you give me some advice?
to flatulent:
I design the circuit just from my personal interest not for sale.Thanks.

 

[guzd]

I had build a board at 66Mhz with 2 layer board.
It works.,but the stability is a problem

 

[Johnson]

To Bluerain..: You need to simulate your board as transmission line with IBIS models of ICs.

Added after 1 minutes:

to guzd: What do you mean with stability? Do you mean SI problems?

 

[rfmw]

@bluerainbow

as a reference look at look my design here:

**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed**


In addition look at these books:

Signal and power integrity in digital systems: TTL, CMOS, and BiCMOS
Digital systems engineering
High speed digital system design : a handbook of interconnect theory and design practices
High-speed digital design : a handbook of black magic
High speed digital system design : a handbook of interconnect theory and design practices
Digital signal integrity : modeling and simulation with interconnects and packages
High-speed digital circuits
MECL System Design Handbook

Most of them are here at the forum. If you need the author's names, let me know.

I believe that 70 MHz is frequency low enough that you wont need termination and not even worry about transmission line impedances. However what is your design and what logic will you be using?

regards,
rfmw

 

[chinara]

Is it for a Ethernet port? I did not find any transformer or RJ45.

 

[rfmw]

Yes, it's for the AUI Ethernet port and does not require any transformers.

 

[jdhar]

I imagine this would be difficult to do without controlled impedance AND without a back ground plane. I think one or the other is definitely needed

 

[eltonjohn]

2 layerss i assume that this is because of a price matter. one thing that you can do is to add copper foil wih some type isolant to one of the sides and ground it .
cheap simple .

 

[ppenday]

yes it will work well. i have done this before and it worked fine.

 

[actra]

dont work with thick boards.. work with FR4...ive done this with higher frequency than urs and it worked...