4 ms·

I really wanted Lime to succeed here, because we could all use the competition, but man, that Lime chip really is absolute crap. It has dead zones all over the

by ohazi 6y ago

I really wanted Lime to succeed here, because we could all use the competition, but man, that Lime chip really is absolute crap. It has dead zones all over the spectrum where the LO PLL won't lock, even within the temperature spec. [1] I returned my LimeSDR Mini after a frustrating weekend and bought a USRP instead, which uses the AD chip, and there's really no comparison. This is one reason why I said in another comment that I thought it'd be difficult for a fabless upstart to complete on a complex / high-performance design like an ADC. The chip Lime designed is an absolute monster -- it has multiple ADCs, DACs, filter banks, switches, oscillators, PLLs. If any one of them isn't perfect, the whole design is shot. I'd still like for them to succeed, but when you're selling a hundred dollar IC, it really does need to be flawless. [1] https://discourse.myriadrf.org/t/new-limesdr-mini-loopback-test-failed/6067 https://discourse.myriadrf.org/t/new-limesdr-mini-loopback-t...

apcragg 6y ago
Those deadzones are horrible. Also, the calibration routine is absolutely broken. For example, when userspace requests a certain TX gain, the chip does some calibration black box magic to determine the best way to distribute that gain across the internal amplifies. Nothing special here, the AD9361 does the same thing. The Lime chip will inexplicably fail the calibration but __will continue to operate__. If the PLL didn't lock, the chip sees something dumb like the loopback being down at -45dBFS so it cranks the gain on all of its internal amplifiers to __correct__ the loss. This results in one or more of the internal amplifiers saturating and you end up with horrible intermod. I was seeing -10dBC ACPR on a simple 1MHz QPSK signal. Sure, you can save off good calibrations or do it by hand, but if the simple loopback cal doesn't work and won't tell the user, the chip is irremediably broken.

by ohazi 6y ago

apcragg 6y ago

Those deadzones are horrible. Also, the calibration routine is absolutely broken. For example, when userspace requests a certain TX gain, the chip does some calibration black box magic to determine the best way to distribute that gain across the internal amplifies. Nothing special here, the AD9361 does the same thing. The Lime chip will inexplicably fail the calibration but __will continue to operate__. If the PLL didn't lock, the chip sees something dumb like the loopback being down at -45dBFS so it cranks the gain on all of its internal amplifiers to __correct__ the loss. This results in one or more of the internal amplifiers saturating and you end up with horrible intermod. I was seeing -10dBC ACPR on a simple 1MHz QPSK signal. Sure, you can save off good calibrations or do it by hand, but if the simple loopback cal doesn't work and won't tell the user, the chip is irremediably broken.