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Recent content by sqx

  1. S

    Noise figure/factor and equivalent noise tempeture

    By defiltration, NF = (N_noise_due_to_input + N_added)/N_due_to_input When we talk about the noise factor of a LNA under a 50 ohm system, is the input noise regarding the thermal noise of a 50 ohm source resistor? So that the output noise due to input source is K*T*B*Gain? But let's say we...
  2. S

    What performance should we look at for a good transconductor stage design?

    If I want to design a good transconductor or Gm-cell for a Gm-C filter, what performance should it have? If I want to use it to build a 2nd order LPF which cuts off at 40 MHz, what bandwidth should the Gm-cell have? Also, people usually only talk about transconductance of the Gm-cell, but what...
  3. S

    Can't find "portAdaptor" in Virtuoso

    Hi, I'm trying to do load pull in Virtuoso, but I can't find the "portAdaptor". It should be in the rfExamples library, but I can't find that library. How should I fix it?
  4. S

    Radiation pattern of an inverted F antenna IFA

    In Balanis' book, the working principle of a inverted F antenna is similar with slot antenna. But why does this the radiation pattern look like a Y-direction placed magnetic dipole? Why isn't it a X-direction placed magnetic dipole? What makes the nulls at +Y and -Y directions? Why is it...
  5. S

    Methods of decreasing the coupling between two closely placed antennas

    When one device has multiple antennas and some of them operate in the same band (like WIFI and Bluetooth), how can we lower the coupling between two closely placed antennas? Is there any rule of thumb for antenna layout or grounding?
  6. S

    Question about Beam forming and MIMO

    Hi, From the view of antenna theory, beam forming means using multiple antennas to create a desired beam, or controlling the beam direction by changing the magnitude and phase of each antenna element. Usually we'll regard all the elements as one antenna when we look at the far field. In...
  7. S

    Dual feed patch antenna with single connector

    I guess you can, as long as you make sure the phase difference doesn't change.
  8. S

    Problem of impedance matching of Gilbert cell mixer

    Hi, For a typical double balanced Gilbert cell, how to match the RF input to 100 ohm? The zero frequency input impedance should be infinity. Even when frequency increases, the input impedance doesn't change significantly at sub-6GHz range. I understand that inductive degeneration can help...
  9. S

    Understanding of noise figure

    Hi, From the equation of cascade noise figure, we can see that the noise figure of the chain is determined by the first several stages of LNA. But how to physically understand it? Why is cascade noise figure set up bu the first several stages?
  10. S

    Dual feed patch antenna with single connector

    you can use delay line or hybrid. Or you can create an array.
  11. S

    question about Friis equation with very large antenna gain

    Hi, in Friis equation, if the gain of transmit and receive antenna are very high, at least from this equation we may have Pr/Pt larger than 1. But since antenna is passive, it's not possible for this ratio to be larger than one. How can I understand this question? Mathematically what is...
  12. S

    In-band image problem for low-IF receiver

    Hi, For a low-IF receiver, how do we deal with the in-band image problem? take this figure for example, say that it's a low-IF receiver with f_IF = 1 MHz. Thus the image for one channel could be another channel, which can't be filtered by your band-selection BPF. Then how do we solve the image...
  13. S

    How does intermodulation affect receiver system?

    Thanks! Can I understand it as IM product of channel 1 and 2 will rise up the noise floor of channel 0, which degrades the sensitivity at channel 0?
  14. S

    How does intermodulation affect receiver system?

    Hi, In receiver design, we care very much about linearity and the IIP3 of the receiver must satisfy some requirements. But how is intermodulation affecting the receiver system? I saw from the BLE 4.2 document that for bluetooth receiver, to measure the IIP3, if the desired frequency is f0, the...
  15. S

    Why should LNA also care about IIP3?

    Thanks! Do you mean that the base station is transmitting signals for A, B and C simultaneously? So all these three signals will arrive at A, which means signals for B and C may be blockers for A?

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