| Electronics > Projects, Designs, and Technical Stuff |
| Level shifting |
| << < (7/11) > >> |
| syntax333:
I couldn't find any information about CSOUT being active low (at http://www.ti.com/lit/ds/symlink/lm1881.pdf section 7.3.1) are you sure about that? |
| Benta:
Page 3. Look at the timing graph. |
| syntax333:
Finally I found time to build the circuit according to your recommendations. The problem was probably due to wrong switch logic and MOSFET as you stated. After I changed the two of them, most of my problems are solved. You can see the final circuit in attachments. I have couple of problems. 1) As you can see from DS1Z_QuickPrint2 and DS1Z_QuickPrint3 signal is degraded. Shouldn't yellow signal and blue signal be the same? Is this due to low resistor value at follower circuit? 2) I get weird random spikes at output of the follower circuits (as seen in DS1Z_QuickPrint1 ) are those little spikes acceptable to an video display device? or should it be as clean as the input signal to follower circuits (blue signal)? (I couldn't find any supplier that sells DG417 in my country however, according to BrianHG's suggestion, I tried to build the circuit with 4066.) Also do you see any other problem at the circuit schematic? |
| syntax333:
I have been able to solve the problem by changing 10kohm at input of the emitter follower with 1k and changing npn emitter follower resistor with 10k instead of 1k. (Yellow signal is AV input signal and blue is output of the buffer) |
| Benta:
Congratulations, very impressive results! After your getting the switch logic fixed, I also see that the LM1881 is now triggering reliably, probably due to better decoupling. The sync/black/blanking levels are just as they should be, great! The attenuation of the color carrier puzzles me. The emitter followers would normally not be able to cause this, they should be fast enough. I'll put my thinking hat on. But thanks for coming back with your results. |
| Navigation |
| Message Index |
| Next page |
| Previous page |