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Recent content by eslavko

  1. E

    Fast step signal generator.

    I have only 250MHz osciloscope. So I can't measure slew rate with it. But I do see ringing of AC14 clearly. So All data I got is from ADC in TDR alone. And maybe I have trouble here. I capture signal with track and hold circuit based with LVC4066 charging capacitor and after that there is buffer...
  2. E

    Fast step signal generator.

    I got little under 2nS with 74LVC4066 and little better with74LVC14. But I have 5 gates paralleled in LVC14 and 4 switches in LVC4066. All drive 50 Ohm resistor. If Drive 5m of twisted pair the LVC14 is the clean winner. Seems that capacitance of twisted pair affect more 4066 than LVC14. Need to...
  3. E

    Fast step signal generator.

    Well TS5A23160 data sheet says: 1.65 to 5.5V supply - Fine for me On state resistance 0.9 Ohm - Perfect for me Bandwidth 100MHz - Probably to low. TurnOn/TurnOff 2.5nS/6nS -That's BAD. (Based on figure 18 that's really propagation delay) I can't find real slew rate. But based on frequency...
  4. E

    Fast step signal generator.

    I do read datasheet. And can't find the switch with Ton or rise time to be under 1nS. I assume when switch is closed the signal can travel fast from source to drain. But when switch is in transition from off to on the gates must be charged and this take more time than signal propagation from...
  5. E

    Fast step signal generator.

    Today I look more on digital switches. But seems that is not good for my application. As I need fast rise time the switch should have one input tied to VCC and output controlled with control input. And that is not situation for what the switch is designed. For example ADG902 can work up to 4.5...
  6. E

    Fast step signal generator.

    I cant find fast enought one. And to be capable to drive 100mA.
  7. E

    Fast step signal generator.

    So to got back on topic. Does someone understand the document in link on the 1st post?!? Figure 3 on have just what I want. So what I get the circuit is common emitter. (and described in text too). As there are no schematic I tried to reverse engineer the pcb on Figure 10. I assume that bottom...
  8. E

    Fast step signal generator.

    I do check analog switches. But seems to be to slow or underpowered. As I need actual line driver for 50/100/120 Ohm cables and up to 1000m long I think all logic ates and similar seems to be out of question. Basic I=U/R give me that driver need to put at least 100mA, but cable act as capacitor...
  9. E

    Fast step signal generator.

    As I'm not sure if PCB layout is the problem I just soldered one 74AC14 like dead bug on piece of blank PCB. It's DIL but I cut the legs so it's onli aprox 1mm long and soldered to ground plane. Vcc is decoupled with 100nF ceramic and 47uF Tantalum. Added one more cap and resistor to make...
  10. E

    Fast step signal generator.

    I have two prototipes. One with THT dil and other SMD. One layer of PCB is ground other vcc and signals. I have decoupled with ceramic and tantalum on each chip. I know that socket is no god but for experimentig I have it. And just replacing HC with AC cause exesive ringing. I assume that AC is...
  11. E

    Fast step signal generator.

    I should explain what is in picture. That is signal response from aprox 5m of twisted pair cable. (I want to make better Time Domain Reflectometer) So the 1st rise is actual step from generator and second one is reflection as cable is not terminated. I do tried with HC, AC, LVC logic but wasn't...
  12. E

    Fast step signal generator.

    FvM that seems good. But my signal from AVR is little slow and as I see there are no schmidt trigger in gate.
  13. E

    Fast step signal generator.

    ...I tried avalanche generator but pulse is to short. I need aprox 30uS long pulse with fast rise time (under 1ns) and don't care :razz: fall time. I was able to extend pulse to 5uS but then got into trouble as there is long charge time for capacitor. And other problem is that triggering...
  14. E

    Fast step signal generator.

    Hello... Actually I need fast rise from 0 to 5V (0 to 4V is OK) with step under 1nS. Then I need steady 5V aprox 30uS long. The fall edge is not important. Then there is recovery time aprox 60uS long. Here is attached image of TDR output. Blue line is with 74AC14, Red line is with 74HC14 and...
  15. E

    Fast step signal generator.

    Hello.... Long time ago I build TDR. It has 47AC14 as pulse generator, but now I want to improve it. AC14 is just little to slow and has excsive ringing. I do search a lot and found that SRD is way to go. (Avalanche generator is other direction as I want step and not pulse) HC14 has no ringing...

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