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  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...
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    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...
  8. 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?
  9. 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...
  10. 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...
  11. 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...
  12. S

    Why should LNA also care about IIP3?

    Usually LNA works in linear region, but some text books and documents say that sometimes there can be "blocker" signals which may force the LNA into non-linear region. My question is what's source of the blocker signals? In my view, when your mobile phone is very near to the base station, the...
  13. S

    Problem about amplifier biasing circuit

    Hi, For CMOS integrated LNA in this picture, is LD a part of the matching network? Usually if LD and C1 is a bias Tee, LD should be a RF choke and C1 should be a DC blocking cap. But such large L and C can't be built on chip. So I assume they are just matching network. But why do we sometimes...
  14. S

    How to calculate Signal Power using ADC samples?

    Hi, I'm going to test the performance of an antenna, but unfortunately the antenna is connected to the receiver front-end and ADC on the board and cannot be separated from the board. So the only way I can read out the signal is to read the data from ADC. Is it possible to convert voltage samples...
  15. S

    GNURadio matched filtering

    Can GNURadio do matched filtering for code? For example the gold code for of GPS signal. Can GNURadio do binary sequence matched filtering? It seems that I can't find any demo online.
  16. S

    Question about transistor on MMIC

    For example we're going to design a power amplifier in ADS, we usually do device simulation then schematic simulation and then layout and EM simulations. In the layout phase, how do people place the transistor on the layout? I just don't understand that when we're doing PCB based design, the...
  17. S

    Question about LNA stability resistor

    To unconditionally stabilize the amplifier, I put a shunt resistor of 25 ohm after the transistor. Since my Vce is 3V, the resistor is going to consume about 0.2W of power. Is this resistor gonna induce very much heat? I just found that the smaller this resistor, the better the stability. But I...
  18. S

    Question about single balanced mixer design

    I'm trying to design a microstrip line based single balanced RF mixer using 90° hybrid and 2 schottky diodes. In this picture, is that matching network going to match the diodes to 50 ohms? I did it in my ADS simulation, but I found that the signal from one diode branch, which makes my...
  19. S

    Question about biasing network of simple RF amplifier

    In this biasing network, what is the RF bypass capacitor for? And what is that resistor R for? My understanding is that the capacitor will prevent RF signals to go to DC source. Is it correct? Somebody told me that the resistor can help with the stability of the amplifier especially at low...
  20. S

    Question about GPS receiver bandwidth

    I'm trying to build a simple GPS receiver using microstrip components. If I'm correct, I think the bandwidth of GPS L1 band is about 25 MHz. I tried to build a 5-order coupled-line filter in ADS with a bandwidth about 50 MHz. I found that it's already been very difficult to realize a 50 MHz...

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