Lms7002m agc/rssi

shao · 8 June 2018 10:26

Hello Lime,

We are trying to setup high power PA and LNA on LimeSDR for the LTE project.

We want to know how to make use of the on-chip AGC. Is it controlled by the RSSI automatically, or do we need to configure in LimeSuiteGUI?

I know there is an option in srsLTE to choose rx_gain automatically, but we are not sure whether it talks with LMS7002 well since there are too many intermediate layers like Soapy.

Thanks!

milo · 8 June 2018 12:40

You might find the following helps:

For MCU AGC testing, there is an option (checkbox) labeled 'Enable MCU
AGC ’ in LimeSuiteGUI ‘TRX Gain tab’.

From code it can be started/stopped using LMS7_Device::MCU_AGCStart()
and LMS7_Device::MCU_AGCStart() functions:

The code that is executed when toggling ‘Enable AGC’ checkbox in
LimeSuiteGUI can be found here:

github.com

myriadrf/LimeSuite/blob/master/src/lms7002_wxgui/lms7002_pnlGains_view.cpp#L150


cmbG_LNA_RFE->Enable(value);
cmbG_TIA_RFE->Enable(value);
cmbG_PGA_RBB->Enable(value);
cmbC_CTL_PGA_RBB->Enable(value);
cmbLOSS_LIN_TXPAD_TRF->Enable(value);
cmbLOSS_MAIN_TXPAD_TRF->Enable(value);
cmbCG_IAMP_TBB->Enable(value);


}


void lms7002_pnlGains_view::OnAGCStateChange(wxCommandEvent& event)
{
if(chkAGC->GetValue() != 0)
{
    LMS7_Device* lms = (LMS7_Device*)lmsControl;
    double crestFactor;
    txtCrestFactor->GetValue().ToDouble(&crestFactor);
    uint32_t wantedRSSI = 87330 / pow(10.0, (3+crestFactor)/20);
    lms->MCU_AGCStart(wantedRSSI);
    txtCrestFactor->Disable();
}

LMS chip settings can not be changed while MCU AGC is running, so MCU
AGC should probably be started after finishing configuring the chip.

shao · 8 June 2018 13:38

Thanks Milo, will try that.

milo · 8 June 2018 14:53

…actually thanks to Lime’s team. They’ve shared these information with us in the past

shao · 9 June 2018 07:23

After reading the documents. I still have some doubts.

According to LimeSDR Made simple series 2. There are 3 stages of amplifiers in the receiving path. primary LNA, RxTIA and RxPGA. Which amplifier stage is the MCU_AGCStart() function actually tuning? And this MCU_AGC is based on the digital rssi instead of the analog rssi right?

ricardas · 9 June 2018 09:19

It uses LNA and PGA stages, and it’s based on digital RSSI

shao · 9 June 2018 10:40

Thanks Ricardas!

shao · 15 June 2018 06:27

Hello Milo,

I enabled the AGC checkbox in LimeSuiteGUI, and then I put a walkie-talkie nearby the LimeSDR, but when I move the walkie-talkie around, the amplitude of its signal on fftviewer is always changing. It is supposed to be maintained almost as constant right?

How do I evaluate the effect of AGC?

Thanks!

shao · 15 June 2018 08:18

It seems to be a version problem.

I was using LimeSuite 18.01 and AGC isn’t working properly.

Now I am using with LimeSuite 18.04 and 18.06, the AGC is working now.

I tested for LimeSDR-USB with walkie-talkie, now it really maintain constant power level regardless of distance. But LimeSDR-Mini seems not supported yet.