PSoC™ 4

[VinayDand]

Hello,

   

We need to generate accurate timing / waveform output using PSoC4 device.

   

PSoC4 does not have a built in crystal oscilltor support.

   

Internal IMO is +-2%, trimmable to certain range, (this is not sufficient and correct compare to crystal oscillator)

   

External crystal oscillators are expensive and consumes more power.

       

Do you have any suggetion on this issue?

       

Regards,

   

Vinay

[Anonymous]

        This is just an idea, I do not ever. Would you use the internal logic INV for the oscillator. This is a feasible idea. I think.   

[Anonymous]

If you have to use internal oscilator and needs low power, then try the PSoC5 LP. 

[Anonymous]

 There are Watchdog chips with watch crstal oscillator which is reasonably low power. You may be able to use the clock signal to trim the internal oscillator. 

[Anonymous]

        Interesting link. http://www.fairchildsemi.com/an/AN/AN-118.pdf   

[ETRO_SSN583]

Some thoughts -

       

1) Use of a onchip gate for OSC element, like shown in  Fairchild Ap Note, is

   

a compromise. First on chip oscillators, device size used, big impact on power.

   

Second there is no temp compensation in a plain vanilla CMOS gate. Third

   

device to device variations impact osc loop, so startup, reliability are all potential

   

problems.

       

2) There is a technique, at manufacturing test, to input, to a pin then counter chain

   

to measure F, a high precision clock of known F. A measurement is made and that

   

determines  a G correction for all future measurements. That of course does not

   

comp for T and V. To do T, a technique used in industry, is to force large currents thru forward

   

biased pin diode, to heat up a part, then swicth to normal mode operation, and take several

   

readings over temp to establish a least squares error curve fit or power equation coef-

   

ficients. V of course is a precision programmable power supply, and it is swept thru a range,

   

and offsets to precision F are recorded and used in future reading interprolation.

       

[Anonymous]

I think your calibration approach is good. However, it would be very time consuming during production.

   

One way to do it is use a external low power oscialltor to generate a 1 hz signal and internally use a counter with the master clock as the input with the 1 HZ as the gate, every second check the deviation of the count and adjust the internal calibation value as needed.

[ETRO_SSN583]

One trades off cost-external components-accuracy-time-precision-architecture-reliability

   

in a design. The approach I show is used extensively in precision test instrumentation,

   

used on our workbench instrumentation..

       

That approach can take out the T & V dependance of your external oscillator.

       

One approach recently, for high accuracy, low cost, use of GPS chips to develop

   

gate. Immune to T and V, but take external components, hence cost and reliability.

       

Buit then we are just speculating, as we do not know what poster needs in performance

   

specifications.........

       

Regards, Dana.

[VinayDand]

Hello,

   

Thanks every one for giving various ideas.

       

More details about our intended project:

   

1) We will not be that keen on low power, as we are now allowed to put hefty battery of up to 800mAH, still a low current consumption will be appreciated.

   

2) We will be generating digital waveform pattern with frequency ranging from 30Hz to 35KHz. Absolute timing accuracy wished will be +-0.008% to +-0.01%. Say e.g. 1 HZ or better at 10000 HZ .

   

(operating product temperature between 15 C to 48 C)

   

3) This will be moderate volume product, so, ease of calibration and time to calibrate should be reasonable.

       

I will appreciate more insight from community in using PSoC4 to achieve the end result.

   

Regards,

   

Vinay

[Anonymous]

        Hi electro, Accuracy you said is +-80ppm to +-100ppm. That is feasible by a simple cristal element. For calibration is need trim-capacitor. When carefully designed will be accomplish the products.   

[Anonymous]

 For this accuracy, the best may be using crystal oscillator. But if cost is an issue, may be a crystal with a low power cmos gate/inverter IC would do the job. Or you can try one of the new MEMS oscillators as well.

[VinayDand]

        Thanks for the suggestion, As we are planning a master main clock frequency of 48MHz, Our external oscillator clock frequency has to be 48MHz, as there is no clock PLL multiplier in to PSoC4. Is this correct or we can try something else? Regards, Vinay   

[ETRO_SSN583]

48 Mhz is the external spec for PSOC 4, that would be the way to

   

achive what you are looking for.

       

Reagards, Dana.

[Anonymous]

Would you consider PSoC3 in this case?

[Anonymous]

        For most micros the external crystal has capacitors on two pins and two connections to the uP. The PSoC4 only has P0_6 as a connection so I am curious of how to use an external crystal with the PSOC4. Please give a reference design if possible...thanks.   

[JoBr_1593366]

    

The PSoC4 only has P0_6 as a connection so I am curious of how to use an external crystal with the PSOC4.

   

   

On the demo board, they use eco_out (P7.1) and eco_in (P7.0) for this, not ext_clk (P0.6).  I'm not sure why these two "external clocks" are on different pins.

[HeLi_263931]

You need to use a crystal oscillator, not just a crystal. For that, single pin is sufficient.

[Anonymous]

 Thank you for that eloquent but simple difference.  I had not caught that before.

   

Sean

[Anonymous]

 As a followup, is there any reason one should not just create a Pierce Oscillator by using an internal device and driving the signal back to the external crystal as shown conceptually in this ap note?

   

http://www.cypress.com/?docID=41149

   

If not, an ap note on best way to implement such would be a great idea for Cypress to do for the PSoC4.

[HeLi_263931]

I think you can implement that. But given the performance of the PSoC4 comparator, I would not use it with a crystal faster than 10MHz (or even maybe 4).

[ETRO_SSN583]

The requirement is for 48 Mhz clock, one would not attemp that with

   

onboard comparator, 150 nS typ response times (componet datasdheet,

   

although conflict, datasheet shows 38 nS, still too slow for 48 Mhz),  rather

   

a CMOS inverter would be used. AN54439 is not a 48 Mhz solution as there

   

is probably not enough G in an internal inverter in linear region to sustain

   

oscillation at 48 Mhz, especially over temp. In any event uncompensated simple

   

inverter would not achieve the accuracy required over any significant temperature

   

range.

       

Some help, attached doc for considerations.

       

Regards, dana.

[ETRO_SSN583]

For earlier question about clocking -

       

[ETRO_SSN583]

Paste did not work, see attached for clocking -

       

Regards, Dana.

[Anonymous]

 Thank you Dana for that explaination.  That really helped.  Considering that I went for the 4 vs the 5lp for cost, that savings just got significantly marginalized.  Guess I should have done more homework. 🙂

[ETRO_SSN583]

Your problem I think still is there using PSOC 4 or 5 LP, because of the

   

100 ppm over temp requirement. Stated another way you still can achieve

   

a lower cost by using PSOC 4.

       

Regards, Dana.