60° phase shifted signals at 2 MHz  - Page 1
Forum section: electronics / rf-microwave

author: knight04
author_rank: Newbie
timestamp: April 02, 2020, 05:28:04 pm
content: Hello everyone !For my PhD project I need to design a high frequency single phased inverter with 60 degrees phase shift between legs control signals (in order to cancel the 3rd harmonic at the output).I found the LTC6909 (datasheet here) which can give 6 outputs phase shifted by 60°. However the frequency with this device is set using an external resistor and not very precise. Hence I'm looking for a programmable (I2C or whatever) clock/oscillator and preferably with a lower jitter than LTC6909 and a higher frequency resolution (5 kHz resolution at around 2 MHz would be enough).So I was wondering if anyone could help me to find such a device please.Thanks in advance

author: KrudyZ
author_rank: Frequent Contributor
timestamp: April 02, 2020, 05:33:19 pm
content: Just use a synthesizer chip with the output frequency set to 12 MHz and some logic to decode the phases.

author: duak
author_rank: Super Contributor
timestamp: April 02, 2020, 06:59:53 pm
content: I cannot remember the trigonometric identiy now, but it is possible to generate a variable phase sinusoid over a range of 0 to 360 degrees from a quadrature (0 and 90 degrees) source by simple summing. ie. arbitrary_ sinusoid = Asin(wt) + Bcos(wt) where A & B are the weightings of the quadrature sinusoids.Generating the quadrature sinusoids could be done with a quadrature Direct Digital Synthesizer such as the AD9854:https://www.analog.com/en/products/ad9854.html#product-overviewThere are simpler, lower performance methods using digital counters and simple filters. There are also analog methods using All-pass filters or Polyphase filters and the above summation technique. What performance do you require?

author: bson
author_rank: Unknown
timestamp: April 02, 2020, 11:55:53 pm
content: A 12 bit circular serial-to-parallel register, like you could make from two 'LVC595s. Load it with 111111000000 using the serial input at startup, say from a small µC. Clock to rotate it at your desired frequency times 12 using an XO. Tap different pins for phases.

author: knight04
author_rank: Newbie
timestamp: April 05, 2020, 06:56:25 am
content: Quote from: KrudyZ on April 02, 2020, 05:33:19 pmThank you very much for your reply and sorry to be a bit late.I made some attemps with simple combinatory logics to have the phase shift but it seems that I has to go throug sequential logic.

author: knight04
author_rank: Newbie
timestamp: April 05, 2020, 07:03:37 am
content: Quote from: duak on April 02, 2020, 06:59:53 pmThank you very much for your reply and sorry to be a bit late.Seems a very interesting way to do. However as my skills in electronics are not very good (that's a shame) i'm not sure if I got it right.What I need for the inverter is for now full wave signals shifted by 60°, so I don't know how to make the link with sine and cosine.Would it be possible to explain it a bit more please ?Thank you very much

author: knight04
author_rank: Newbie
timestamp: April 05, 2020, 07:18:26 am
content: Quote from: bson on April 02, 2020, 11:55:53 pmThank you very much for your reply and sorry to be a bit late.I'm not very good in electronics unfortunately. I think I see how to do. I'll try to do some simulations to see if I can have the phase shift.

author: KrudyZ
author_rank: Frequent Contributor
timestamp: April 05, 2020, 05:14:05 pm
content: I'm curious what subject your PhD is in?From your responses I can only assume it's not EE, but I wonder why you would need to design a HF inverter in a different field.Is it just to help with some experiment?If so, maybe it's better to look at off-the-shelf solutions.

author: duak
author_rank: Super Contributor
timestamp: April 06, 2020, 08:00:18 pm
content: knight04,I am sorry, I did not see that this circuit is for an inverter. I thought it was for something in the RF field.One simple digital circuit is the ring or Johnson counter. Here is a link to an explanation with some examples:http://www.idc-online.com/technical_references/pdfs/data_communications/Ring_Counters.pdfPlease note that a four stage counter generates edges 90 degrees apart, while six stages generate edges 60 degrees apart. Note also that a higher frequency clock of the number of stages x fout is required. eg., 12 MHz is required for a 2 MHz output with six stages.

author: Xnke
author_rank: Regular Contributor
timestamp: April 07, 2020, 04:33:01 pm
content: SI5351 will do what you want, but you'll need an amplifier to do it.On top of that you can tweak your phase shift to whatever you need.There are 1, 3, and 8 output versions-the cheap 3 output version will do what you want and outputs up to +8dBm to drive your amplifier. It's I2C/SPI controlled and there is LOADS of usage data out there.Just +3.3V, GND, and I2C bus in, 3 SMA ports out.https://www.adafruit.com/product/2045The above is one 8$ example, and there is programming information as well. Easy to get.