Schematics Review of the Fine Delay module.

The mail below includes most of the review comments of the review held on 17 August 2010

From: Matthieu Cattin
Sent: Wednesday 18 August 2010 10:50
To: Grzegorz Kasprowicz
Cc: Erik Van Der Bij; Pablo Alvarez Sanchez; Tomasz Wlostowski; Maciej
Fimiarz
Subject: Re: RE : FW: Fine Delay FMC

Hi,

On Tue, 17 Aug 2010, Grzegorz Kasprowicz wrote:

On 17 August 2010 23:22, Matthieu Cattin <> wrote:

Hi Greg,

Here are my comments:

FMC delay top:
- LED2 (PLL_STATUS from U_clock_generator) is not connected.

sure, it should be renamed to LED1, fixed

I'd rather use this LED to indicate an input trigger than the PLL status.
What do you think?

- LA06_P, LA01_N_CC and LA01_P_CC (I2C bus for thermometer and Si570)
are not connected to the FMC connector.

anyway, this generator will be removed due to its cost.
Since we have PLL there is no need to have adjustable clock.
simple 25MHz , preferably TCXO oscillator would do the job.
Thermometer will be connected directly to the I2C bus of the FMC card - it
is addressable.

OK.

- PD (AD9516 pin 24) is active low and is connected to GND, the chip is
always powered down. => PD has an internal pull-up.

OK,so there is a bug in a library - it is not marked as active low.

The symbol is OK, but there is an option in Altium called "Single '\'
Negation" that should be activated in DXP > Preferences > Schematic > Graphical Editing

- SYNC (AD9516 pin 8) is active low too. => SYCN has an internal pull-up.

OK, the resistor can be not soldered then or removed

As SYNC is not used, I think you can remove the resistor.

- Is REF_SEL useful as the reference input is differential?

Ok, my fault.
Since TCXO has single ended output, now REF2 can be used as ext clock. But
FMC does not provide any SE clock source. Shall we use this option at all ?
I connected it mainly because I had double switch :)

You can always connect REF2 to an FMC data line.
But I don't see any use for it.

- BTW, why using a Si570 as reference for the AD9516?

I don't remember, there was a discussion about it. At that moment I didn't
plan a PLL at all. It will be replaced by low cost crystal since we have
PLL.

OK.

TDC:
- I don't understand the VDDC_TDC regulator connection.
Shouldn't VDDC_TDC be connected to 3.3V?

It is correct - I copied this from working device - BPIM board that I did
for CMS.
We discovered that it locks faster when both voltages are regulated by
internal PLL.

Ok, good to know.

Output buffer:
- The OE (output enable) logic looks strange to me.
Shouldn't you use an OR gate and connect OEn to RESET instead of RESETn?
This would disable the outputs during reset and on request (calibration).

well, it depends if you want to have output disable signal active low or
high.
At the moment both of them are active low.
But you are right - using OR gate is safer.
But even better is using NAND - both inputs must be high to enable. And such
component exist in CERN library.
So during reset phase outputs will be disabled.
I added pull-down resistor to it.

We can use a NAND gate then. But you'll have to rename OUTPUT_DISABLE into
OUTPUT_ENABLE.

General:
- The functional specification says "1 input, selectable between front
panel
and FMC connector" but I don't see the input from the FMC. Or do I missed
something?

Oh, it's me who missed it.

As you said, we can use a analog mux here.

Cheers,

Matthieu