Amplifier 1W into 50 \$\Omega\$, BW=50MHz min, gain x2 or more - Page 1
Forum section: electronics / projects

author: Jester
author_rank: Frequent Contributor
timestamp: November 06, 2016, 04:03:10 pm
content: Amplifier 1W into 50, BW=50MHz min, gain = x2 or betterDoes not have to be super precise or low noise.Am I better to purchase as a unit or could I cobble something together with common parts?

author: joeqsmith
author_rank: Super Contributor
timestamp: November 06, 2016, 04:15:16 pm
content: I bought a kit some time back that I used to test my P6042 current probe. I posted some pictures here of the build. Much higher power and BW that you need but building a kit may be an option.

author: Jester
author_rank: Frequent Contributor
timestamp: November 06, 2016, 06:44:23 pm
content: Quote from: joeqsmith on November 06, 2016, 04:15:16 pmJoe, can you provide a link to the kit?

author: joeqsmith
author_rank: Super Contributor
timestamp: November 06, 2016, 07:21:25 pm
content: Quote from: Jester on November 06, 2016, 06:44:23 pmNo problem. Here's the link showing the amp and a link where I bought the kit from:https://www.eevblog.com/forum/projects/home-made-pa-and-load/msg640180/#msg640180

author: danadak
author_rank: Super Contributor
timestamp: November 07, 2016, 01:50:50 am
content: A possibility -http://www.w1ghz.org/small_proj/Simple_Broadband_Power_Amplifiers.pdfhttp://dl5dbm.darc.de/6mpa100.pdfhttp://ae6pm.com/Semidata_books/Motorola/DL110_rev13.pdfRegards, Dana.

author: David Hess
author_rank: Super Contributor
timestamp: November 07, 2016, 04:25:52 am
content: Quote from: Jester on November 06, 2016, 04:03:10 pm1 watt into 50 ohms is 7 volts and 141mA.There are lots of discrete designs which can handle that reasonably to 50 MHz but they require some experience to design and implement.TheLinear Technology LT1206high power current feedback amplifier can handle your requirements and comes in an easy to use 8 pin DIP or TO-220-7 package. The larger TO-220-7 package may be required to handle the power dissipation depending on the average output power. The LT1206 is reasonably priced for this application if you are not prepared to do a discrete design.

author: GK
author_rank: Super Contributor
timestamp: November 07, 2016, 06:26:08 am
content: Quote from: David Hess on November 07, 2016, 04:25:52 am10V peak (1W/50R) requires a slew rate of 3142V/us. LT1026 is specified at 900V/uS.EDIT: That's to do 50 MHz.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 07, 2016, 08:23:17 am
content: A somewhat meatier example from my lab,http://seventransistorlabs.com/Images/Wideband_Amp_4W_50MHz_Sch.pnghttp://seventransistorlabs.com/Images/Wideband_Amp_4W_50MHz.jpgThe basic circuit is pretty simple. Though, I realize, now that I've drawn it out, it uses rather more components than most (clocking in at 55 parts, plus doubles, plus a few fiddly bits of connection on the real build).Anyway, it's a gain stage, emitter follower to drive the MOSFET gate, and output coupling.You can think of it as an extension of a conventional audio amplifier. There's too much phase shift to have feedback around the whole thing, so it's capacitor and transformer coupled, between individual stages. Each stage has internal feedback, which helps keep distortion down.Note the use of transmission line transformers. L1 "doesn't do anything", on account of both ends being wired in phase (and therefore not needing a magnetic core, either). But it matches the delay with L4, which does invert phase.The gain stage is built like an inverting op-amp (1k feedback, 100 ohm input resistor = voltage gain of 10 = 20dB), so it terminates the source (which is 100 ohms per side, both sides in parallel is 50 ohms at the connector) as well as providing flat gain.The 2SC3595s are able to shove around the MOSFET gates fairly well, pushing the small-signal bandwidth to around 50MHz. The 47 ohm bias resistor is quite wasteful, and isn't even enough: the full-power bandwidth is less, showing that the gates aren't fully turning off. Two booster stages would be ideal, with the second one being a complementary buffer (class AB to save quiescent current).Good luck finding 2SC3595s, by the way; fast, non-RF power transistors are far and few between these days! Probably a few SOT-89 RF transistors would be the nearest substitute, but I doubt they'd price very well either...The output coupling consists of one transmission line between drains (doing the duty of a CT inductor), and another that reassembles the two phases into one. The negative side is flipped positive (thus having one voltage drop along its length), and the positive side is stacked on top (thus having one voltage drop along its length). Since the voltage drops are equal, the winding lengths and turns counts can be the same, too, which makes the transformer design nice and simple.I forget what the LF cutoff is, probably something like 30kHz.Tim

author: Jester
author_rank: Frequent Contributor
timestamp: November 07, 2016, 12:45:01 pm
content: Quote from: David Hess on November 07, 2016, 04:25:52 amI'm going to add a LT1026 to my next Digi-Key order.

author: David Hess
author_rank: Super Contributor
timestamp: November 07, 2016, 12:47:08 pm
content: Quote from: GK on November 07, 2016, 06:26:08 amWell, that was embarrassing. Thanks for pointing it out.