RF Design - The Designer's Guide Community Forum
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RF Design - The Designer's Guide Community Forumen-usThe Designer's Guide Community ForumThu, 18 Jul 2019 11:14:52 +0000http://blogs.law.harvard.edu/tech/rss30Value of DC block capacitor in LNA
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The Designer's Guide Community Forum/RF Designhttps://designers-guide.org/forum/YaBB.pl?num=1561007833Hi <br /><br />I am designing a 2GHz common gate CMOS lna and need to add DC block capacitor at its input i.e. source of input MOS.<br /> <br />I have come to know that value of this cap should be approx. 2Ohm to avoid adding high impedance in signal path at desired frequency which if calculated using formula 2-Ω= 1/ωC at 2GHz; value for dc block cap comes out to be 39.8pF. <br /><br />Is this the right way to calculate value for DC block cap in LNA rfic ? What if I used smaller value say 5 or 10pF. Will it disturb my input matching since I have dc biased input CG MOS such that it gives gm=20mS resulting in 50-Ohm impedance at its source and LNA input.<br /><br />Regards<br />VipulNF simulation using out-of-band blocker (SpectreRF)
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The Designer's Guide Community Forum/RF Designhttps://designers-guide.org/forum/YaBB.pl?num=1558447008Switched capacitor filter? I have no idea why you would have a switched capacitor filter in this simulation, but its clock will cause a lot of problems. You should eliminate it if you can.<br /><br />Conceptually an LNA with a blocker is very much like a mixer where you are interested in the direct transmission path (no frequency conversion). In this case the blocker plays the role of the LO. So apply the blocker as a large sinusoid on the input. Apply the input signal as a small stimulus (using pacmag), also on the input. Run PSS at the blocker frequency. Run PAC at the input frequency and set the sideband to 0.<br /><br />-KenMoved: Verilog-A Oscillator Phase noise
https://designers-guide.org/forum/YaBB.pl?num=1555313951
The Designer's Guide Community Forum/RF Designhttps://designers-guide.org/forum/YaBB.pl?num=1555313951This Topic has been moved to <a href="https://designers-guide.org/forum/YaBB.pl?num=1555313950/0">RF Simulators</a> by Ken Kundert.PFD phase noise
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The Designer's Guide Community Forum/RF Designhttps://designers-guide.org/forum/YaBB.pl?num=1553848087Sorry, I was thinking about the output of the charge pump. The charge pump injects noise into the loop filter as long as the current sources are on.<br /><br />-KenSmith chart of λ/4 Transmission Line
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The Designer's Guide Community Forum/RF Designhttps://designers-guide.org/forum/YaBB.pl?num=1552919615Hi...<br /><br />1. The location of the Zin and Zout on smith chart will depends on the impedance values. In the attached smith chart, I think, the locations were chosen randomly.<br />But from figure, you can observe that Zin>Zout and both are real (pure resistances).<br /><br />3. Yes. In quarter-wave transformer case, ZTline is geometric mean of Zout and Zin.<br />You can observe this result by simply substituting l=lambda/4 in basic "transmission line impedance equation".<br /><br />4. Question can be more clear.<br />but scaling with Zo (50ohm) is for simplicity. it is like, ZTline is normalized with Zo (ZTline/Zo).<br /> <br />Regards...Designing a low noise amplifier using AWR microwave office (Newbie/Student)
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The Designer's Guide Community Forum/RF Designhttps://designers-guide.org/forum/YaBB.pl?num=1551816668Hello,<br /><br />First of all, i want to know about the subcircuit you are using in the design. whether it is just S2P file? or it is an amplifier model provided by the vendor?<br /><br />Form the datasheet, i can understand that, you no need to add extra transmission lines and tuning (internally matched to 50 ohm).<br />you just need to follow the circuit provided in the datasheet (2nd page).<br /><br />Coming to your schematic, you connected Vcc and RFout directly. In general, we should use decoupling capacitors for RF IN and RF OUT (1nF as shown in datasheet).<br /><br />Just add add capacitors at input and output (as shown in datasheet) and simulate. you should get some positive gain.<br /><br />Comment back with simulation results...High-pass Wilkinson Power Splitter
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The Designer's Guide Community Forum/RF Designhttps://designers-guide.org/forum/YaBB.pl?num=1552518235Hi Guys, I'm designing a Wilkinson power splitter to work around 160 MHz using lumped element components. I've designed the splitter as per the standard design procedure for a series L / shunt C topology (values are 13pF, 27pF, 68nH) and it works well. However I need to add some high pass filtering to my circuit and I'm wondering can I design a high pass version of the wilkinson splitter (instead of the standard low pass version) to combine the two functions? I've added some high pass filtering in before the splitter but my in-band insertion loss becomes too high.<br /><br />Does anyone know where would I find how to do the calcs for this, if it's possible?<br /><br />Many thanks,<br />DaveQuestion on Hajimiri-Lee model
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The Designer's Guide Community Forum/RF Designhttps://designers-guide.org/forum/YaBB.pl?num=1549266425This is a good question and deserves a more nuanced answer. The impulse as you have drawn it at t1 does indeed produce both phase and amplitude, changes, but will mostly produce phase and a little bit of amplitude shift. However, there exist an impulse near the transition point for the ideal LC that would produce only phase shift with no net amplitude change (as long as the instantaneous voltage change is not greater than twice the amplitude of the oscillation). The exact location of such an impulse depends on its size. This can be seen from the time-domain waveform shown and the corresponding state-space diagram, shown in the attachment, and can be verified both analytically or using simulations. Now, the smaller this impulse is relative to the oscillation amplitude, the closer the point with zero net amplitude change will be to the zero crossing point. In the limit of an infinitesimal impulse it will be exactly at the zero-crossing point, making that point have zero phase sensitivity from a perturbation perspective. This is not an issue in practice since the model was developed for noise, which in almost all cases can be viewed as a small perturbation.<br /><br />You also raised another good question about the energetics of this impulse response and how it can induce no amplitude change (namely no change in the net energy of the tank). There is no contradiction here. The answer is that the impulse has a fixed charge (its net area) not necessarily a constant energy. More precisely, the instantaneous power delivered to the tank is the product of the instantaneous tank voltage and the injected current. For the injection shown in the attachment, the voltage is negative for half of the infinitesimal cycle and positive for the other half so the integral (the total power delivered) is actually zero. If you have trouble seeing this, assume that impulse is a short pulse with a non-zero width. So there is no inconsistency here. No net energy is delivered to the tank and thus no net change in the tank amplitude will be observed. <br /><br />One of the replies to your question on this forum that cites another paper requires some additional clarification. The original paper describing the ISF-based model published in the February 1998 issue of JSSC, offers a model based on the ISF. The model is accurate for phase noise calculation as long as the ISF in determined accurately. The accuracy of this model and its mathematical equivalence have been shown to hold independently by others as well. In addition to the full discussion of the model and its implications for the design, the original paper also offers three methods to determine the ISF in the order of accuracy in an Appendix. The first method (method A) of the appendix is based on direct evaluation of the ISF based on injection of small impulses and measurement of the resultant phase shift. The next two methods are approximations based on some simplified analysis. The paper clearly states that method A "is the most accurate of the three methods presented." The approximate methods B and C are just that, approximations to calculate the ISF. Now the validity of the primary approach of the paper is not affected by the method used to calculated the ISF, it is just a question of accuracy of the method used to calculate the ISF. If method A is used to calculate the ISF, the results are correct, accurate, and intuitive. Even the cited paper by the commenter clearly states that "The first method, a direct calculation in SPICE, with an impulse swept through offsets from a reference point in the oscillator waveform, is correct." Again the point of the other paper is related to the accuracy of the method used to calculate the exact ISF, not the general result of the model. Methods B and C are quick simplifications that may or may not be useful in determining a useful estimate of the ISF, and as simplifications they are by definition "wrong". This is somewhat similar to stating that pi is 3.14 and somebody responding: "Since it is proven that pi is irrational and 3.14=157/50, i.e., a rational number, this is wrong." It does not make 3.14 as useless as -56.8. That is the nature of approximation, which people who design generally appreciate. But regardless, even that inaccuracy is in some of the possible methods of calculating the ISF, not the model itself.<br /><br />I guess the key take away is that as long as you calculate the ISF correctly (for example using method A), the qualitative and quantitative results obtained from the proposed approach are accurate. Also the insight obtained from the general properties of the oscillator and how its phase noise behave in response to design changes are not affect by the choice of the method used to calculate the ISF.<br /><br />In a follow-on post, you ask two additional questions, which I try to answer quickly while I am here:<br />1. ISF is unitless, because radian is unites. It is defined as the ratio of two lengths (the length of the arc facing an angle in a circle divided by the radius.). So as a ratio it is unitless; No inconsistency.<br />2. The ISF can be determined for any kind of tank. For an ideal (as you put it lossless) tank, it can be determined analytically as a closed-form solution for small perturbation (e.g., noise). The choice of tank Q, will affect the shape of the ISF through oscillation waveform change, and will affect the in^2/Df in the form of the noise it introduces. <br /><br />I hope you find this helpful.RF Distribution basic question
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The Designer's Guide Community Forum/RF Designhttps://designers-guide.org/forum/YaBB.pl?num=1551106618Hi guys!! <img src="https://designers-guide.org/forum/Templates/Forum/default/smiley.gif" border="0" alt="Smiley" /><br /><br />I'm trying to design a RF distribution for my wireless receivers.<br /><br />I'm a sound recordist working in TV, so I have to deal with wireless microphones daily. <br /><br />Basically the setup I would like to have is 2 dipole antennae connected to my 2 wireless microphone receivers.<br /><br />I am working in UHF band, 470 to 600MHz. <br /><br />I am using mini-circuits components, SMD, and the distribution has to fit in a tiny 3cmX3cmX1cm.<br /><br />I am a sound engineer, I have very limited knowledge in RF and analog circuits. I try to read and watch tutorials, but I get lost very quickly as I don't speak the basics of this language. In theory, the circuit is suppose to work. The problem is when I look a the schematic of the components (Balun and Splitter), I don't understand which how to connect every thing together, as I am not able to read the schematic. <br /><br />So, it would go like this ; <br /><br />Dipole antenna -> Balun -> 2 way Power Splitter - 2X female SMAs output -> wireless receivers. <br /><br />The question ; I know this is elementary school for most of you, I just need someone to point me out which pins to connect where. Like the actual circuit path. <br /><br />I got myself a mini-circuit 1:1 transformer and a 2 way power splitter. I am good at soldering, but I just don't know technically how to connect everything. <br /><br />Here is my thinking, please tell me where I am wrong;<br /><br />So we start with the 2 Dipole elements, one goes in the Primary of the balun, the other one goes in the secondary. <br /><br />At the other side of the balun, Primary Dot becomes my main "signal", Secondary Dot connects to ground of the hole circuit. <br /><br />Then my main signal enters the "S" port of the splitter, and the splitter is attached to ground that carries the signal from the other sides of the dipole (?)<br /><br />Then at the exit of the Splitter, I attach 2 SMAs, that are grounded as well. <br /><br />Here below the schematic of my 2 units. <br /><br />Balun ; <br /><br /><a href="https://imgur.com/a/UKALki2" target="_blank">https://imgur.com/a/UKALki2</a><br /><br /><a href="https://www.minicircuits.com/pdfs/ADTL2-18+.pdf" target="_blank">https://www.minicircuits.com/pdfs/ADTL2-18+.pdf</a><br /><br />Splitter ; <br /><br /><a href="https://imgur.com/a/YezoLGL" target="_blank">https://imgur.com/a/YezoLGL</a><br /><br /><a href="https://www.minicircuits.com/pdfs/ADP-2-9+.pdf" target="_blank">https://www.minicircuits.com/pdfs/ADP-2-9+.pdf</a><br /><br /> <br />Thank you so much!!<br /><br />SimonRF Inductor Layout
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The Designer's Guide Community Forum/RF Designhttps://designers-guide.org/forum/YaBB.pl?num=1550285780Hi,<br /><br />I am currently doing a layout for an RF 2.4GHz receiver in GF 130nm CMOS technology using Cadence Virtuoso. I have begun planning my layout and I have some general questions regarding the inductors.<br /><br />I have two single-ended inductors about 18nH (pretty large area, an outer diameter of 300um for both of them) which are connected to a cross-coupled CMOS pair to form the differential LC oscillator. There is also a varactor across the pair for frequency tuning. <br /><br />I am trying to determine a reasonable space between the inductors and the varactor/nfets. In the training document, the only information I found was the spacing between the bond pads and the inductor. Reading Alan Hastings book I couldn't really find any information on this. The inductors are at the highest metal levels (MA, E1). Could anyone help assist with the following questions:<br /><br />1) Related material for inductor layout<br /><br />2) General spacing and area rules besides the DRC<br /><br />Thank you. <br />