A Fully Integrated CMOS Active Bandpass Filter for Multiband RF Front-Ends - Page 1
Forum section: electronics / projects

author: promach
author_rank: Frequent Contributor
timestamp: November 22, 2020, 05:01:57 pm
content: ForA Fully Integrated CMOS Active Bandpass Filter for Multiband RF Front-Ends, why does the following circuit show highpass characteristic instead of bandpass characteristic ?

author: promach
author_rank: Frequent Contributor
timestamp: November 25, 2020, 10:57:21 pm
content: See attached themodified LTSpice circuit filethat shows *some* bandpass characteristicsHowever, the bandpass peak still have some issue with gain.

author: Wimberleytech
author_rank: Super Contributor
timestamp: November 28, 2020, 09:51:41 pm
content: A couple of things.1) I am pretty sure that the paper has a typo. When it said length/width, I am pretty sure it meant width/length. But that is not the killer issue IMO.2) Did you look at your operating point voltages at all nodes? How did they look? (Hint...not good...you just blew up your computer and your house).3) Related to #2...you have six ideal current current sources in your simulation. That can lead to (and does in your sim) bad stuff.I was able to make your circuit kinda work by fixing the w/l values and adjusting the ideal current sources.Rule: NEVER EVER EVER trust an ac simulation without validating the operating point. This is true for simulations and the lab bench

author: promach
author_rank: Frequent Contributor
timestamp: November 29, 2020, 01:03:57 am
content: Problem solved, but with high power consumption (45uW). Seehttps://github.com/promach/active_bandpass_filterBut how to1. Decrease the high power consumption (45uW) without affecting much on the gain2. Determine the mathematical expression for deriving the bandpass cutoff frequency more precisely

author: Wimberleytech
author_rank: Super Contributor
timestamp: November 29, 2020, 01:26:39 pm
content: Great progress! My fix was achieved by increasing abia1/4 to 4uA as well!As far as deriving the expression...might be a lot of work...I will see if I can get around to it.

author: Wimberleytech
author_rank: Super Contributor
timestamp: November 29, 2020, 03:02:52 pm
content: I think you can eliminate M7 and M8 and IQ2. The circuits are in parallel

author: promach
author_rank: Frequent Contributor
timestamp: December 02, 2020, 08:43:55 am
content: 1) why the increase of both current source values will increase the centre frequency ?2) are there ways other than increasing current source (which increases power consumption) ?3) I suppose the gyrator used in this active cmos bandpass filter circuit is a shunt inductor ? So, how does this actually lead to bandpass filtering effect ?4) I am trying to study about the following. Could anyone explain about it ?

author: Wimberleytech
author_rank: Super Contributor
timestamp: December 02, 2020, 02:25:14 pm
content: Which current source values?I know that you know this: gm is a function of root(I). So naturally current is going to change gm and thus everything gm affects.

author: promach
author_rank: Frequent Contributor
timestamp: December 10, 2020, 03:13:58 pm
content: QuoteIncrease both Ibia1 and Ibia4I am still quite unsure how this circuit works as bandpass filter

author: promach
author_rank: Frequent Contributor
timestamp: January 02, 2021, 02:41:15 pm
content: Let's start with the gyrator/active inductor (which is part of the active bandpass filter) analysis :How to derive the inductive impedance (or expression 2.25) of the following active inductor topology ?Here is therelevant book chapterwritten by the same circuit creator.

author: mawyatt
author_rank: Super Contributor
timestamp: January 03, 2021, 05:54:29 pm
content: Long ago we abandoned filters based upon "synthesized active inductors" due to the limited dynamic range and poor noise performance, same reason with non-Foster networks. One of the many reasons the PolyPhase Mixer (PPM), N-Path Mixer or Mixer First topologies were so attractive with better than theoretical mixer noise figure, excellent DR and antenna port tuning without inductors (R +- jX reactance synthesized from baseband RC networks without active elements), which happens to tune with the LO without varactors or other tuning elements, and places a narrowband bandpass filter as "seen" at the antenna port without an actual bandpass filter!https://www.eevblog.com/forum/rf-microwave/polyphase-or-n-path-mixer/Best & Happy New Year,

author: promach
author_rank: Frequent Contributor
timestamp: January 11, 2021, 12:19:46 pm
content: Just curious, how exactly doesMixer-First topologyplaces anarrowband bandpass filteras "seen" at the antenna portwithout an actual bandpass filter?