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Recent content by Antenna94

  1. A

    180° hybrid phase balance

    Hi! I am currently designing a double-balanced microwave mixer (9...10GHz) and was wondering about 180° hybrids. What phase balance would you consider acceptable i.e. not significantly deteriorating mixer performance. I couldn't find any rules of thumb. My initial design is 177...183° in the...
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    PLL active loop filter for relatively high minimum tuning voltage

    Because the varactors have a high 0...30V tuning range, however, feedback filter Q changes with tuning so I can't use the whole range. Another reason is that electric length is a function of frequency and the phase shift of the feedback path cannot be approx. constant for a wider band, so I had...
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    PLL active loop filter for relatively high minimum tuning voltage

    It is a school project, the emphasis is on the development and study of the microwave VCO, the PLL is just an enhancement for it - if your question was that why don't I use a PLL with VCO integrated. Otherwise, the PLL will be an IC, only the loop filter has to be realized with external...
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    PLL active loop filter for relatively high minimum tuning voltage

    Hi! I have designed and built a VCO with a 12...25V tuning range and I would like to design an active loop filter for an integer PLL IC to control the VCO frequency. I would need some advice, help, or just verification that my train of thought is not wrong. The charge pump output can produce a...
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    RF Filters designing

    Hi! Basically the same, but the resonators in a hairpin filter are bent into a "U" shape in order to use less space.
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    Amplifier singularity

    Hi! I am designing an oscillator and its amplifier has some interesting characteristics (picture enclosed). There are some frequencies where the Rollett factor has a local maximum, and at these frequencies the transistor does not amplify at all. (It is not a matched amplifier as it is to be...
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    Analog PLL design, mixer as phase detector

    Maybe my question isn't clear, or I just don't see the answer in the replies. I am asking if it is possible to use a transistor mixer as a phase detector, no charge pump. I understand that there is "no need to use the capacitor to block the output of the mixer", but then the DC bias of the...
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    Analog PLL design, mixer as phase detector

    FvM but then how can you ensure that the output is DC coupled but the bias voltage doesn't get out? Or we cannot use a transistor mixer as a phase detector, only diodes?
  9. A

    Analog PLL design, mixer as phase detector

    Hi! I'm trying to design an analog PLL for fun with about 25 or 50MHz frequency. I was planning to use a Gilbert-cell mixer as a phase detector, but I have a question. A transistor mixer needs a bias circuit, and that should be decoupled from the other parts of the circuit. But by using...
  10. A

    DC blocking at high frequencies (10GHz)

    The problem with chip capacitors is that at 10GHz for good decoupling I would need at least 3pF (<5ohm reactance), and those bigger values have resonance and/or bad Q at high frequencies. volker@melhaus: thank you! It seems to provide good coupling, but I though that in MMIC design these...
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    DC blocking at high frequencies (10GHz)

    Now I am a bit baffled. As the characteristic impedance of the system will be 50ohms, I thought the reactance of the DC-blocking capacitor at the working frequency should be at most 5ohms, so the capacitance has to be greater than 3pF at 10GHz. I designed an interdigital capacitor based on AWR...
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    DC blocking at high frequencies (10GHz)

    Thank you everyone for the useful insights! Meanwhile I managed to achieve 1.5dB coupling, but the width of the lines is much smaller than that of a 50ohm line and it just seems unlikely that a 50ohm line continued in a 100ohm coupled line pair (100ohm being the stand-alone impedance of one line...
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    DC blocking at high frequencies (10GHz)

    Thank you! I also heard that theoretically full coupling (0dB) should be able with a coupled transmission line pair. Is that true? (It seems impossible.)
  14. A

    DC blocking at high frequencies (10GHz)

    Hi! I'm designing a circuit at 10GHz and have a bit of a problem with DC blocking. I can't seem to find capacitors with high enough capacitance (in 3pF would give ~5ohms reactance at 10GHz which would be fine in a 50ohm system) and SRF. Another thought was to use coupled lines as DC blocks, but...
  15. A

    Mixer conversion loss across input power level

    In the saturation region Id is dependent on Vgs^2 (diplexed input signals applied to the gate). But in the linear region among others it depends on Vds^2 and Vds*Vgs. So it is only linear for a fixed Vgs, but it is not so in a mixer. This configuration is also called a multiplier type mixer. It...
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