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  1. R

    Reading list for very high speed PCBs (>7 GHz bandwidth)

    Hello, Can you suggest a book/reading material that can teach about how to design high speed PCBs for signal transmission? Due to an unfortunate turn of events, I now have to design PCBs with >7GHz bandwidth per line for fiber-optic front-end interface. Hence I think I have to learn about the...
  2. R

    CPW simulation in ADS using momentum and co-sim

    Hi all, i found some discrepancies when simulating a CPW in ADS momentum compared to when co-simulating in ADS the same layout. Wonders if someone can help clarify things. It's a bit involved so I thank you so very much for your patience. Situation: We are simulating a coplanar waveguide...
  3. R

    Refractive index of solder mask

    unfortunately i have no simple ways of measuring it. was hoping that there is a datasheet somewhere that gives the refractive index of solder mask.
  4. R

    Is the S21 plot result given in the voltage ratio or the power ratio in ADS Momentum?

    Re: S21 in ADS Momentum thanks for the replies. I did some tests on ADS and i think that S21 gives the voltage ratio when we display the S21 in terms of its magnitude (V0/V1). But if we display the S21 in terms of dB, it's converted into 20*log(V0/V1), so the plot in dB is the same for power or...
  5. R

    How can I simulate resistor in MOMENTUM LAYOUT?

    I dont know how to do EM co simulation between momentum layout-ADS schematic. Is there a tutorial on this somewhere? Thanks
  6. R

    Coplanar waveguide sandwiched between GND and VCC

    Hi A question about coplanar waveguides (CPW). A conventional CPW structure is a signal line sandwiched between two ground tracks. Can we get the same characteristic impedance if we sandwich a signal line with the same dimensions between a GND track and a VCC (some DC supply voltage, say +5V)...
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    Is the S21 plot result given in the voltage ratio or the power ratio in ADS Momentum?

    Hi, Just a simple question. Is the S21 plot result we get from momentum in dB the voltage ratio or the power ratio? Is there a method to convert one to another in ADS? Thanks!
  8. R

    Refractive index of solder mask

    Hello, Does anyone know what's the typical refractive index of a green solder solder mask material? Guess that this is not a typical question but we need the value for some optical system design. Cant seem to get the value from web. Thnx!
  9. R

    Stiff PCB material with similar dielectric constant as FR4

    Re: Stiff PCB material? thanks for the replies. It's ok if it's not too expensive. It just have to be available commercially. I am however constrained by having to use double sided, single layered PCB since the final design must be lowest cost possible. i've tried using copper fill in the...
  10. R

    Stiff PCB material with similar dielectric constant as FR4

    Hi all, My 1 mm FR4 board warps all over the place when heated. Do u know of a cheap PCB substrate with similar dielectric constant to FR4 but is stiffer? Thanks
  11. R

    High frequency noise for 10 Gbps circuit

    Hi, Thanks for the replies. I've been away for a while so I could not work on this. To summarize, these are the things that I should try right? 1. Put 22 uF capacitor after regulator - biff 2. Put the bypass caps closer - biff 3. 10 kOhm resistor to GND on PD - biff 4. Use combination of 1pF...
  12. R

    very low noise 3.3 V voltage regulator

    Hi, At the moment I am trying to design a very low noise power supply for a 7GHz comms circuit. The best power design I got is based on ADP3338 attached below. The circuits require 3.3V and takes in 150 mA current max. The smaller the voltage regulator circuit is, the better. Have u got a...
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    SNR - peak-to-peak or RMS?

    Hi, Hope someone can help me with the definition of signal-to-noise ratio (SNR). On the last page of this document: https://pdfserv.maxim-ic.com/en/an/AN607.pdf it is said that SNR is the ratio of the peak-to-peak signal and the rms noise However, wikipedia...
  14. R

    Output impedance matching question

    Re: Output impedance Hi, silly me...i think my simplified circuit is wrong. The picture below is the actual circuit that I wanted to ask about. In this case is the output impedance 50 Ohm? and why?
  15. R

    High frequency noise for 10 Gbps circuit

    hi and thanks for the reply c5,c6 are within 15 mm to the driver chip c8,c9 are within 2 mm to the driver chip all have direct via connection to the ground plane big pad of the laser driver is soldered to a ground pad with 4 direct via connections to the ground plane register is set so that...
  16. R

    Output impedance matching question

    Output impedance Hi I came across this voltage source (attached below) but i am unsure what its output impedance is. Is it 50 Ohm and hence must be matched with 50 ohm transmission line and load? How do we proof its output impedance mathematically? thanks in advance!
  17. R

    High frequency noise for 10 Gbps circuit

    Hi thanks for your replies I measure the eye diagram from the electrical output of a high speed receiver photodiode. I attached a laser (VCSEL) to the laser driver circuit and coupled the emitted light to this high speed receiver. Not sure what the extinction ratio is but that is the optimum...
  18. R

    parasitic extraction from PCB layout

    hi is there a software that can extract parasitics (LRC parameters) given a PCB layout? thanks
  19. R

    High frequency noise for 10 Gbps circuit

    Hi, I am designing a 10 Gbps laser driver using commercially available ICs. At the moment, I noticed that there is significant noise in the resulting eye diagram. This noise is reduced when I touch the circuit (to be precise, the interface line between the IC and the laser) with my bare hands -...

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