Controllable gain power amplifier - Page 1
Forum section: electronics / projects

author: promach
author_rank: Frequent Contributor
timestamp: February 23, 2020, 02:21:00 am
content: What isng?What are the purposes of Ctrl0, Ctrl1, Ctrl2 and Ctrl3 ?

author: awallin
author_rank: Frequent Contributor
timestamp: February 23, 2020, 07:16:06 am
content: a simple view might be that the upper FETs work as "variable drain-resistors" for the lower FETs?

author: magic
author_rank: Super Contributor
timestamp: February 23, 2020, 07:55:10 am
content: ng is obviously W divided by 9µ. Seriously, no ideaI think the upper FETs and Ctrl inputs are used to cascode the lower FETs or to disable them (by strapping Ctrl to ground) and thus reduce gain.

author: promach
author_rank: Frequent Contributor
timestamp: February 23, 2020, 12:02:59 pm
content: What about L_stage1 and Bias2 ?Should I just connect these two to Vdd ?

author: Miti
author_rank: Super Contributor
timestamp: February 23, 2020, 12:20:37 pm
content: L means inductor to me. Most likely you need to connect an inductor series with a bias resistor to set the correct bias voltage on both L_stage1 and RFout. Bias2 sets the bias voltage (thus the current) for the final stage.

author: filssavi
author_rank: Frequent Contributor
timestamp: February 23, 2020, 12:34:35 pm
content: This is an integrated circuit schematicW and L are the gate physical length and width ng is the number of parallel gates (basically this is done for matching since multiple equal gates are affected by things such as doping concentrations and etch rates in the same way)Ctrl are almost certainly digital signals that are used to trim biasing or gain of the block (the more you turn on the more current you have)EDIT: the more I look at it the more it looks like some sort of a variable gain amplifier

author: promach
author_rank: Frequent Contributor
timestamp: February 23, 2020, 02:29:17 pm
content: QuoteYou were referring to L_stage1. What aboutBIAS2?

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 23, 2020, 03:02:29 pm
content: So yeah as blueskull said, ng here is the number of parallel devices (transistors), it's a very common way of defining transistors on a microelectronics schematic. This parameter is more commonly called "m" though (as in "multiplier"). L and W are the gate length and gate width respectively.If you haven't learned the basics of semiconductors, reading this kind of schematic will be tough. You can start here:https://ecee.colorado.edu/~bart/book/book/chapter7/ch7_2.htmIf you have but are just confused with "ng", then see above.As to the schematic itself, it's basically a series of cascode amplifiers. You can start here for the basics:https://en.wikipedia.org/wiki/Cascode, and then read the additional links.The Ctrlx signals will modulate the overall gain.

author: promach
author_rank: Frequent Contributor
timestamp: February 23, 2020, 03:10:38 pm
content: I was asking about L_Stage1 and Bias2

author: promach
author_rank: Frequent Contributor
timestamp: February 23, 2020, 05:01:31 pm
content: Wait, this variable gain amplifier does not fall into anyclass of RF Power Amplifier?

author: rfeecs
author_rank: Frequent Contributor
timestamp: February 23, 2020, 07:03:54 pm
content: The gain (transconductance) is proportional to the width of the FET. Ctrl0 to Ctrl3 turns each of the four FETs on or off, changing the total gate width and consequently the gain.The width would be W x ng. So you have widths of 36, 144, 324 and 900 that can be switched. Plus M1 has a width of 81. I wonder how they came up with those sizes. I would have expected a binary sequence, maybe.As mentioned, L_stage1 would be an inductor to bias the drain of stage 1.