• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 96 subscribers
  • Views 392 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DM6437: CLKOUT and VCLK

Anonymous
Anonymous

Hi,

I would like to ask a question with DM6437 clock output.

 

For two clock outputs: (1) CLKOUT (2) VCLK:

Although datasheet both listed their voltage group as IPD-DVDD33, the actual output voltage as measured by oscilloscope significantly exceeds that value.

In addition, there are also negative values when CLKOUT output 27MHz without division. Although at this time the frequency is the same as the crystal input, VPP has changed from 1.8V to 4.88V, and the most negative value being -640mV.

Question 1

It's reasonable for the amplitude to change since the output clock signal has gone through the internal circuit of DM6437. However, why would VPP be approximately 1.5 times DVDD33?

Question 2

Is the output square wave or sinusoid?

  1. When clock division is not used, the 27MHz output looks close to sinusoid but too being too sharp.
  2. When clock division is used:
    1. 13.5MHz: there is obvious slope as well as somewhat "flat" top, and the waveform is halfway between sinusoid and square.
    2. 4.5MHz and 2.7MHz: looks purely square wave.

Where there looks like a transition from sinusoid → square wave, as frequency ↑?

 

Zheng

  • Anonymous
    0 Anonymous

    Update:

    Probably the spikes observed, especially with 27MHz clock, is due to artifacts of the digital oscilloscope. The VPP measured (13.5MHz, 4.52V), (4MHz, 4.56V), (2.7MHz, 5.28V) cannot be used to represent the nominal voltage level of the output since waveform is not perfect. For {13.5MHz, 4MHz, 2.7MHz }, visually we can see that the average of the "high" part minus "average" of the low part is approximately 3.3V.