Low noise amplifier Puns

How does a LNA eliminate noise and only amplify signal can anyone please explain??

I have a RF background and have designed a few front end cascades. I’ve noticed ADI, Qorvo, etc advertising low phase noise amplifiers.

I have a good understanding of conventional LNAs and understand the role of phase noise in mixed signal systems.

How are low PN amps constructed? What separates them from a conventional LNA?

Thanks!

Hi everyone,

I need some basic advice for impedance matching: I have a photodetector (Det01CFC from Thorlabs, https://www.thorlabs.com/drawings/275cb418cdc2cf1f-A2E46103-D9C0-3581-4553E3D3CA93AD83/DET01CFC-Manual.pdf) that generates a current. For my experiment, I would like to amplify this signal with an amplifier to subsequently read it out with a digital oscilloscope.

The amplifier that I use is the LNA-1440 (https://rfbayinc.com/products_pdf/product_88.pdf) with an input impedance of 50 Ohm. Since the input impedance of the amplifier matches the source impedance of the photodetector, I connected them directly with an SMA-cable.

The problem that I am facing right now is that the signal gets attenuated for frequencies larger than a few MHz, i.e. it seems as if my circuit acts as a low pass filter. Do you have an idea why this could be the case?

Thank you very much for your advice!

I mean those little SPF5189 between the sdr-tlr and the antenna. Thanks in advance, i am quite new with sdr hardware. I was just thinking it could improve the quality of the signal. Or perhaps doesn't work that way. I don't know what i need to buy!

Wanted some help creating the necessary biasing circuitry for an LNA. I've been referring to the Gray and Meyer textbook for some of the topologies, but am having trouble sizing the transistors in Cadence to meet the biasing needs. What are some things to consider when creating this circuitry, more specifically for setting the operating point for the LNA transistors?

My current setup is a Topping A90 as the headphone amplifier and the DAC I am using with the amp, is the Chord Mojo. I know it is not a DAC issue because when I have the DAC turned off, the buzz is still there, but maybe I'm wrong?

If anyone has had this same typical bzzzzzzzzzzzzz sound issue and found a solution, please let me know that would be great! thank you for your time

This is the pcb from my Alpine MRP-M500 mono amplifer that powers the subwoofer in my car. The problem that I have been having with it is that after about 20 minutes of use it starts making a high pitched whine. once this starts powercycling it does not stop the whine, and it is only when the car has been off for a while that the 20 minutes seems to restart. Ocasionaly the noise will stop or start fluttering after it has started, but it always ends up comming back. I have isolated anything but the board as being the problem, as it continues to whine with the subwoofer and signal wires disconected. I have also determined that it is the large transformer with the copper band that is causing the noise. My question is what should I replace to fix it? Is it definitly the transformer that is bad, or could bad capacitors on the board cause the transformer to whine?

https://preview.redd.it/z0dl26d7prc81.jpg?width=1512&format=pjpg&auto=webp&s=58e0d1df910575b3c9d03040376f6ab46bcafcb2

I’ve tried searching around for this but haven’t found much.

I’m hearing a white noise that almost sounds like speaker static but may also be a fan. It sounds like it’s coming from where my windshield meets my dash.

It happens even when the engine is off and the car is stopped. Even if I turn off the head unit and HVAC. Not coming from the engine bay.

Is this fan noise from the head unit? I have the optional 8 inch screen upgrade. It’s pretty loud and I’ve never heard a car do this. I haven’t tested to see if it goes off after X minutes of having the head unit off. It seems to come on when electrical power to the car is on.

I had the dealer add the Rockford upgrade before I picked it up (so I haven’t experienced the stock system). Which I believe includes an amplifier that sits behind the factory head unit. I wonder if that also has a fan - or if something the install is throwing off some static noise.

Thanks all. At least the car smells good.

Hi

I want to use my esp-wroom-32 to measure a low voltage signal. There are 2 amplifier pins, pin 36 and 39. I can't find any information in the datasheet on how to active the amplification. Any tips?

Ive been building my own LNAs for use with software defined radios and they work with TV as well (its the same general band of frequencies) However I usually design them for a target impedance of 50 ohms because that is standard for VHF/UHF communications (because thats the approximate impedance of a quarter wave vertical whip) 75 ohms (the approximate impedance of a dipole) is the standard for TV - basically the traces are a bit thinner.

It seems to me that CATV LNAs I've tried have not been very good. There are much better devices out there. They would probably make excellent LNAs for home TV viewing (I use low cost MMIC devices that have noise figures under 1 db well into the GHz range.)

Do cordcutters ever use LNAs that are meant for amateur radio/telecommunications? Presumably they would be far superior to the front ends in much consumer electronics gear.

I'd like to match an input coil (SP6P5-20-ABW) to 50 ohms and have it resonate at 100MHz. Then I'd like the gate of the FET (ATF-55143) to be matched to 50 ohms looking back at the coil. The main requirement is having as little noise as possible and have it immune to crosstalk from multiple other coils that are in a similar setup. The 50 ohms is a valued picked so that the phase changes and so that the coil can be interchanged and still be matched with the FET, like a universal connection to the pre-amp.

I'm having difficulty understanding how to breakdown each stage for impedance matching so I thought I'd ask you guys.

I'd prefer it in this arrangment if it's possible. Thanks for any suggestions!

I'm making a Deacy amp but in a (large) pedal enclosure. https://imgur.com/a/e7BgRRb

The amp is the amp stage from an old 18v 1960s portable radio. I'm powering the amp using a powerbank with 5v/2.4a outputs plugged into a usb buck/booster which steps up the voltage to 18v. The positive and negative wires from the booster then go to the amp but I've put an on/off switch in the positive wire to break the circuit.

The problem is that the buck/booster creates a horrible whining/bubbling noise that comes out of the speaker. However, when I put a finger on one of the terminals of the (engaged) switch, the noise goes and the sound out of the speaker is nice and clean. It also cleans up when I put one probe of a DMM on the switch terminal.

It's not sustainable for me to keep a finger on the switch terminal not least because I'm probably getting low key electrocuted. Is there another way to cure this noise? I suspect my body/the DMM is behaving like some sort of resistor or capacitor...is that what I need?

Other info: I've attached a crocodile clip jumper cable to one of the switch terminals and attached the other end to various places; me - again the noise clears up; the enclosure - sparks, voltage drops on buck booster; ground on the guitar input - drops on buck booster. The voltage between the switch terminal and ground on the guitar input measures 18v as expected.

Hello - I am researching a topic for my Physics of Semiconductor Graduate Class. I hope this is a good place to brainstorm/discuss. My topic centers on the design decisions behind low phase noise RF/Microwave amplifiers (not LNAs - e.g. Hittite HMC-C050). If there are any engineers out there willing to help my brainstorming - I'd appreciate comments/suggestions.

A few brainstorming questions:

1. Why would Hittite (in this example) build this circuit on GaAs? I've always read that GaAs has a higher shot noise then other semiconductors.... Wouldn’t another semiconductor be better suited for this application?

2. Why would Hittite use a HBT process for this application? Why not a FET-like solution (read: MESFET)? Do bipolars intrinsically have better phase noise characteristics w.r.t. FETs?

3. Does the feedback circuitry involved in distributive amplifiers aid in the phase noise characteristics? I noticed that the P1dB isn’t 10dB less than IP3 – meaning there’s a feedback mechanism in the circuitry. Or did they designing it as a distributive amplifier for the sole purpose of hitting the wide bandwidth specs?

Finally I wonder - what as a systems engineer would I benefit from by purchasing this amp as opposed to a regular old wide-band LNA? Hittite definitely sells amplifiers with much lower noise figure over similar bandwidths. What sets these "low phase noise" amplifiers apart? Why are they worth it (assuming I never compress my amps)?

Thanks for any thoughts. Much appreciated.