- 26th December 2008, 09:26 #1

- Join Date
- Apr 2005
- Posts
- 284
- Helped
- 5 / 5
- Points
- 2,789
- Level
- 12

## clock ppm

anyone tell me "clock frequency is 50MHz+/-50ppm?" what is really frequency?

(50M+ 50/1,000,000)Hz? or (50M - 50/1,000,000)Hz?

50/1,000,000 is very small ,almost can be ignored . I think.

- 26th December 2008, 09:36 #2

- Join Date
- Aug 2008
- Location
- Hyderabad, Andhra Pradesh, India
- Posts
- 1,256
- Helped
- 248 / 248
- Points
- 10,757
- Level
- 24

## ppm clock

You are right but this small time when accumulated over years then it creates an error of second per say.

Some people may not interested in this error too.

For the above calculation the frequency will lie between the two possible frequencies.

- 26th December 2008, 09:36

- 26th December 2008, 09:48 #3

- Join Date
- Jan 2008
- Location
- Bochum, Germany
- Posts
- 27,933
- Helped
- 8811 / 8811
- Points
- 172,245
- Level
- 98

## clock ppm calculation

50 ppm at 50 MHz means a deviation of 2.5 kHz, an amount that isn't really small for a lot of applications.

For a watch, 50 ppm implies an error of 26 minutes per year, for an UHF small band radio device, it would be considerably above tolerated error limits.

- 2nd January 2009, 03:21 #4

- Join Date
- Apr 2005
- Posts
- 284
- Helped
- 5 / 5
- Points
- 2,789
- Level
- 12

## clock ppm calculator

if the samle frequency and different ppm in write clock and read clock ,Anyone can tell me how to calculate fifo depth ?

- 2nd January 2009, 03:21

- 2nd January 2009, 07:00 #5

- Join Date
- May 2007
- Posts
- 31
- Helped
- 4 / 4
- Points
- 1,545
- Level
- 8

## clock frequency ppm

hi feel_on_on

i think if you meet case that different ppm in write clock and read clock, u have to consider worse case to calculate fifo depth.

littlebu

- 6th January 2009, 04:41 #6

- Join Date
- Apr 2005
- Posts
- 284
- Helped
- 5 / 5
- Points
- 2,789
- Level
- 12

## how to compute ppm in clocks

if read clock is 50Mhz+/-50ppm,write clock is 50Mhz+/-50ppm ,but they is the different clock . please tell me how to think about the fifo depth?

Added after 1 hours 57 minutes:

forget to speak ,the MAX transmit Unit is 1500 bytes

- 6th January 2009, 04:53 #7

- Join Date
- Oct 2008
- Location
- Hyderabad
- Posts
- 70
- Helped
- 5 / 5
- Points
- 1,466
- Level
- 8

## what is clock ppm

Originally Posted by**FvM****Sir u have told deviation of 2.5 kHz, can i know with what formula u have calculated that......thanq u**

- 6th January 2009, 06:41 #8

- Join Date
- Jan 2008
- Location
- Bochum, Germany
- Posts
- 27,933
- Helped
- 8811 / 8811
- Points
- 172,245
- Level
- 98

## 50ppm

50e-6*50e6=2500

- 16th February 2011, 00:34 #9

- Join Date
- Feb 2011
- Posts
- 1
- Helped
- 0 / 0
- Points
- 332
- Level
- 3

## Re: clock frequency is 50MHz+/-50ppm?

Here is how to calculate

Convert ppm to Hz

50 MHz nominal +/-50 ppm

(50000000 / 1000000)*50 = +/- 2500 Hz which define the frequency bound of

the oscillator to 49.9975 MHz <= f <= 50.0025 MHz

Hope this will help

- 26th July 2012, 08:00 #10

- Join Date
- Nov 2008
- Posts
- 4
- Helped
- 0 / 0
- Points
- 933
- Level
- 6

## Re: clock frequency is 50MHz+/-50ppm?

Friends check this link for PPM to Hz and vice - versa conversion:

http://www.jittertime.com/resources/ppmcalc.shtml