stable-amplitude sine in the range 100KHz – 10Mhz - Page 1
Forum section: electronics / projects

author: JonathanTee
author_rank: Newbie
timestamp: December 05, 2022, 11:05:54 am
content: Hi everyone! My question is rather practical than theoretical.I am planning the measurement which should last about one year under room temperature, and within it, I need a source of the stable-amplitude sine signal in the range 100KHz – 10Mhz.The most important for me is the stability of the amplitude value. For example, I wouldn’t care if instead of 5 Volts it outputs 5.05V, if this value does not change more than 0.2% over the year every time I switch on the device.The first idea would be to take the common arbitrary signal generator, but all of them (Keysights, Tektronix, R&S) have an amplitude accuracy of +-1%, which is quite a bit too high for me. However, the datasheets do not really mention how stable is this error, which gives me hope that the error may be stable. There is a term "stability" in some of the datasheets (usually 1ppm), but normally it refers to time-axis, isn't it?Lords of the measurements, I summon you. Maybe there is someone really experienced with the stability of AWGs, or someone who knows another off-the-shelf solution.Thanks to everyone who read it! PS. have attached a few datasheets of AWGs

author: David Hess
author_rank: Super Contributor
timestamp: December 05, 2022, 04:15:45 pm
content: Check out page 63 ofLinear Technology application note 47where Jim Williams discusses two examples of RF leveling loops which will correct for variations of input, time, and temperature.

author: mawyatt
author_rank: Super Contributor
timestamp: December 05, 2022, 06:03:12 pm
content: Interesting requirement, and likely not shown in typical AWG data sheets as mentioned.Would think a quality AWG might be able to maintain this level over time if properly operated and environment maintained. One could perform a long term experiment using a high quality SA to verify the AWG performance over time.Best,

author: TimFox
author_rank: Super Contributor
timestamp: December 05, 2022, 07:32:10 pm
content: I would think a good DDS-based synthesizer in that frequency range would be amplitude-stable over time.There are cheap modules available that use the AD9850 DDS:https://www.analog.com/media/en/technical-documentation/data-sheets/AD9850.pdfThe ADI spec sheet does not quote long-term stability, since most users are more interested in harmonics, spurious outputs, and phase noise.Myguessis that running a 125 MHz clock rate to obtain a 10 MHz or lower output would be safe for your purpose, with a stable power supply.

author: nfmax
author_rank: Super Contributor
timestamp: December 05, 2022, 07:40:56 pm
content: Have you tried asking the AWG manufacturers direct? This sort of non-standard pre-sales support question is one of the things that distinguish the 'A' brands from the others

author: TimFox
author_rank: Super Contributor
timestamp: December 05, 2022, 08:36:03 pm
content: Quote from: mawyatt on December 05, 2022, 06:03:12 pmSpectrum analyzers' amplitude accuracy depends on their calibration, which often uses an internal standard generator.That shifts the original question to the long-term stability of that generator.Again, most users are more interested in the time/frequency/phase accuracy, so this may not be covered in the specification sheet.

author: Someone
author_rank: Super Contributor
timestamp: December 05, 2022, 09:42:29 pm
content: Close the loop yourself with a thermal power sensor? Guaranteed specifications get close but not quite to 0.2%Generally when there is a demand for tight accuracy in level, you should consider taking an approach that can use a relative/ratio rather than absolute measurement.

author: jwet
author_rank: Frequent Contributor
timestamp: December 06, 2022, 01:00:35 am
content: Another good option for this frequency range is to make the measurement ratio metric- kind of VNA style. Use a power splitter (mini circuits or roll your own) to get two signals from the Sig Gen, use one as a reference and put the other signal through the DUT. Make a ratio metric measurement with a signal analyzer or decent VNA. The amplitude of the generator drops out of the equations at least to first order.

author: moffy
author_rank: Super Contributor
timestamp: December 07, 2022, 11:14:54 am
content: I have an idea that might work in measuring the 100kHz to 10MHz sine output. It uses an RF dual transistor, BFU520Y, to clamp one side of the cycle and the output is then filtered and measured. A capacitor C4 across the input resistor needs to be trimmable to compensate for HF attenuation, it would be adjusted so that for the same signal level at 100kHz and 10MHz the DC output is the same. The second transistor in the package is used as a temperature sensor to control a heater so that the BFU520Y is kept at a constant temperature. You would want the filtered output to control a gain element so that the signal level is kept constant. There are some issues like how you do the initial calibration of C4 to get a truly flat response. Might be worth a try.P.S. Component values are chosen for convenience, the 2SC4083 model was chosen for convenience, the BFU520Y should perform similar or better.