RF RANGING PERFORMANCE REDUCED FROM 90M TO 40M - NEEDED HELP - Page 1
Forum section: electronics / general

author: Anirudh_THABJUL_SB
author_rank: Contributor
timestamp: August 29, 2016, 09:40:42 am
content: Hello Everyone,I am Anirudh THABJUL, an Electronic engineer working for a company called "SECOND BRIDGE", We are based on Paris.In our applications, We are measuring distance between two 10 layer PCB's through 802.15.4 protocol. To achieve this, We are using mainly1. IMX6 Processor (Main processor)2. SAM4E (Secondary processor)3. RF215 + Antennas for RF ranging sectionOur issue is when we just measured distance between two PCB by putting the IMX6 in ideal state we are able to range upto 90M(Refer the attachment1)but when we activate the IMX6, ranging is reducing to 40M (50 % performance reduction).Can anyone explain this RF interference phenomenon? If possible please suggest us the possible ways to solve this problem like some reference sites or some reference documents?Thank you.Regards,Anirudh THABJUL

author: Kilrah
author_rank: Unknown
timestamp: August 29, 2016, 09:43:13 am
content: Likely EMI from the processor. Might need shielding, power supply filtering improvements, PCB layout improvements...Also don't post duplicate topics.

author: Anirudh_THABJUL_SB
author_rank: Contributor
timestamp: August 29, 2016, 10:01:17 am
content: Hello Kilrah,Thank you for your reply. I have removed other duplicate post. I am sorry i am new to this group.We ahave mentioned"Might need shielding, power supply filtering improvements, PCB layout improvements"Can you please share some more info if you have like some online links or document attachments aboutpower supply filtering improvements?Thank you.

author: VK5RC
author_rank: Unknown
timestamp: August 29, 2016, 10:22:13 am
content: Does the RF share any power components e.g. +/- voltage rail or ground with the microprocessor?I have seen some designs where the RF has its own linear regulator and isolated ground as well.

author: Anirudh_THABJUL_SB
author_rank: Contributor
timestamp: August 29, 2016, 10:51:24 am
content: Hello VK5RC,Thank you for your reply.Yes the RF share the Positive and negative power component tracks. So is there a way to fix this issue on existing prototype itself.

author: Edsoncan
author_rank: Newbie
timestamp: August 29, 2016, 11:02:48 am
content: Do you have spectrum analyzer?If is it possible that the EMI can affect the TXO frequency?Are you using a pcb antenna or a cable antenna?

author: bitslice
author_rank: Frequent Contributor
timestamp: August 29, 2016, 11:04:44 am
content: (not an RF person)Something I've noticed in other people's RF designs is that every chip or semiconductor is linked to the power rail via an inductor, presumably to filter out power rail noise.I'd probably stick a uP inside a metal canAnother technique I've seen is to use a spread spectrum design for the uP clock

author: Psi
author_rank: Super Contributor
timestamp: August 29, 2016, 11:09:07 am
content: Try with the IMX6 running at a few different clock frequency, it may simply be your IMX6 clock is a harmonic of the RF frequency.

author: Anirudh_THABJUL_SB
author_rank: Contributor
timestamp: August 29, 2016, 11:16:35 am
content: Unfortunately, We don't have spectrum analyzer with us. We are using four ceramic antenna like in the image attached below.

author: Anirudh_THABJUL_SB
author_rank: Contributor
timestamp: August 29, 2016, 11:18:12 am
content: Quote from: Psi on August 29, 2016, 11:09:07 amHello Psi,Thank you for your reply. We will definitely try this technique.

author: Ice-Tea
author_rank: Super Contributor
timestamp: August 29, 2016, 11:42:43 am
content: Sounds a lot like you're coupling digital noise from the uC into your RF. Have you measured the power supply noise at the RF part with/without the uC active?

author: Edsoncan
author_rank: Newbie
timestamp: August 29, 2016, 11:44:57 am
content: You calculated the mca? (micro channel)Your antenna traces are so thin...

author: Anirudh_THABJUL_SB
author_rank: Contributor
timestamp: August 29, 2016, 11:45:45 am
content: Quote from: Ice-Tea on August 29, 2016, 11:42:43 amNot yet, We will try to calculate it. Can you please explain me what can we conclude exactly after all the noise calculations?

author: Anirudh_THABJUL_SB
author_rank: Contributor
timestamp: August 29, 2016, 11:48:02 am
content: Quote from: Edsoncan on August 29, 2016, 11:44:57 amDo you mean be impedence matching? If yes, Yes we have maintained track widths as per the calculations proposed after imepedence calculations.

author: Edsoncan
author_rank: Newbie
timestamp: August 29, 2016, 12:17:20 pm
content: I am sorry my english is not good.I refer Coplanar Waveguidehttps://en.wikipedia.org/wiki/Coplanar_waveguide

author: Ice-Tea
author_rank: Super Contributor
timestamp: August 29, 2016, 12:34:06 pm
content: Quote from: Anirudh_THABJUL_SB on August 29, 2016, 11:45:45 amCalculate? No, measure. With a decent scope. The PDN (Power Delivery Network) to your RF part must be as clean as possible. If your digital part shares the same network, it will inject noise on the power rail, which will end up in the RF part and which is most likely degrading your RF noisefloor.

author: nctnico
author_rank: Super Contributor
timestamp: August 29, 2016, 02:26:20 pm
content: I second the suggestion of filtering the power supply to the RF section. A spectrum analyser may be a cheaper than a multi-GHz oscilloscope and you can connect a 50 Ohm active or passive probe to a spectrum analyser to look at the spectrum present in a PCB trace.I'm also missing lots of vias to stitch the top copper pours to the inner ground plane. The top copper pour which is supposed to be the coplanar waveguide ground may be acting as an antenna as well.

author: Gribo
author_rank: Frequent Contributor
timestamp: August 29, 2016, 08:42:32 pm
content: Few more comments regarding your design:Your RF traces are long and travel in unnecessary bends and twists. Keep them as short and as straight as possible.Add shielding vias to the ground on both sides of the RF traces, for 2.4GHz, roughly 1cm between each via.Try soldering an SMA connector instead of your ceramic antenna, and see if you get the required output power, with a spectrum analyzer.

author: Ice-Tea
author_rank: Super Contributor
timestamp: August 29, 2016, 08:51:02 pm
content: You may also want to check if you can read out stuff like noisefloor, RSSI, SNR from you device and check with/without the uC active.