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Improve spectrum analyzer

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- revert LO2 shift mechanism (restores previous SA speed)
- allow tracking generator to reach all(?) frequencies with sufficient accuracy
This commit is contained in:
Jan Käberich 2025-01-04 16:50:20 +01:00
parent 8df7d1b7be
commit b77ba278de
3 changed files with 68 additions and 60 deletions
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26
Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnadriver.cpp
View file

@ -501,32 +501,6 @@ bool LibreVNADriver::setSA(const DeviceDriver::SASettings &s, std::function<void
p.spectrumSettings.syncMode = (int) sync;
p.spectrumSettings.syncMaster = syncMaster ? 1 : 0;
if(p.spectrumSettings.trackingGenerator && p.spectrumSettings.f_stop >= 25000000) {
// Check point spacing.
// The highband PLL used as the tracking generator is not able to reach every frequency exactly. This
// could lead to sharp drops in the spectrum at certain frequencies. If the span is wide enough with
// respect to the point number, it is ensured that every displayed point has at least one sample with
// a reachable PLL frequency in it. Display a warning message if this is not the case with the current
// settings.
auto pointSpacing = (p.spectrumSettings.f_stop - p.spectrumSettings.f_start) / (p.spectrumSettings.pointNum - 1);
// The frequency resolution of the PLL is frequency dependent (due to PLL divider).
// This code assumes some knowledge of the actual hardware and probably should be moved
// onto the device at some point
double minSpacing = 25000;
auto stop = p.spectrumSettings.f_stop;
while(stop <= 3000000000) {
minSpacing /= 2;
stop *= 2;
}
if(pointSpacing < minSpacing) {
auto requiredMinSpan = minSpacing * (p.spectrumSettings.pointNum - 1);
auto message = QString() + "Due to PLL limitations, the tracking generator can not reach every frequency exactly. "
"With your current span, this could result in the signal not being detected at some bands. A minimum"
" span of " + Unit::ToString(requiredMinSpan, "Hz", " kMG") + " is recommended at this stop frequency.";
InformationBox::ShowMessage("Warning", message, "TrackingGeneratorSpanTooSmallWarning");
}
}
return SendPacket(p, [=](TransmissionResult r){
if(cb) {
cb(r == TransmissionResult::Ack);

11
Software/VNA_embedded/Application/Drivers/Si5351C.cpp
View file

@ -219,17 +219,6 @@ bool Si5351C::WritePLLConfig(PLLConfig config, PLL pll) {
} else {
success &=SetBits(Reg::PLLInputSource, mask);
}
// Reset the PLL
mask = pll == PLL::A ? 0x20 : 0x80;
//success &=SetBits(Reg::PLLReset, mask);
reg = pll == PLL::A ? Reg::MSNA_CONFIG : Reg::MSNB_CONFIG;
for(uint8_t i=0;i<8;i++) {
uint8_t readback;
ReadRegister((Reg)((int)reg + i), &readback);
LOG_DEBUG("PLL readback %d: 0x%02x", i, readback);
}
return success;
}

91
Software/VNA_embedded/Application/SpectrumAnalyzer.cpp
View file

@ -44,6 +44,17 @@ static uint64_t firstPointTime;
static bool firstPoint; // indicates the first point to be transmitted to the GUI, sets the firstPointTime
static bool zerospan;
static uint32_t PLLRefFreqs[] = {HW::PLLRef, HW::PLLRef - 1000000};
static constexpr uint8_t PLLRefFreqsNum = sizeof(PLLRefFreqs)/sizeof(PLLRefFreqs[0]);
static uint8_t PLLRefIndex;
static void setPLLReference() {
Si5351.SetCLK(SiChannel::Source, PLLRefFreqs[PLLRefIndex], Si5351C::PLL::A, Si5351C::DriveStrength::mA8);
Si5351.SetCLK(SiChannel::LO1, PLLRefFreqs[PLLRefIndex], Si5351C::PLL::A, Si5351C::DriveStrength::mA8);
Source.SetReference(PLLRefFreqs[PLLRefIndex], false, 1, false);
LO1.SetReference(PLLRefFreqs[PLLRefIndex], false, 1, false);
}
static void StartNextSample() {
uint64_t freq = s.f_start + (s.f_stop - s.f_start) * pointCnt / (points - 1);
freq = Cal::FrequencyCorrectionToDevice(freq);
@ -65,33 +76,61 @@ static void StartNextSample() {
negativeDFT = true;
// set tracking generator to default values
trackingFreq = 0;
trackingLowband = false;
attenuator = 0;
// this is the first step in each point, update tracking generator if enabled
if (s.trackingGenerator) {
auto oldTrackingFreq = trackingFreq;
trackingFreq = freq + s.trackingGeneratorOffset;
if(trackingFreq > 0 && trackingFreq <= (int64_t) HW::Info.limits_maxFreq) {
// tracking frequency is valid, calculate required settings and select band
auto amplitude = HW::GetAmplitudeSettings(s.trackingPower, trackingFreq, s.applySourceCorrection, s.trackingGeneratorPort);
// only set the flag here, it is reset at the beginning of each sweep (this makes sure it is set if any of the points are not reached by the TG)
if(amplitude.unlevel) {
HW::SetOutputUnlevel(true);
}
attenuator = amplitude.attenuator;
if(trackingFreq < HW::BandSwitchFrequency) {
Si5351.SetCLK(SiChannel::LowbandSource, trackingFreq, Si5351C::PLL::B, amplitude.lowBandPower);
FPGA::Disable(FPGA::Periphery::SourceChip);
FPGA::Disable(FPGA::Periphery::SourceRF);
trackingLowband = true;
} else {
Source.SetFrequency(trackingFreq);
Source.SetPowerOutA(amplitude.highBandPower, true);
FPGA::Enable(FPGA::Periphery::SourceChip);
FPGA::Enable(FPGA::Periphery::SourceRF);
trackingLowband = false;
// selected power potentially changed, update default registers
FPGA::WriteMAX2871Default(Source.GetRegisters());
if(trackingFreq != oldTrackingFreq) {
// need to change the source frequency
oldTrackingFreq = trackingFreq;
if(trackingFreq > 0 && trackingFreq <= (int64_t) HW::Info.limits_maxFreq) {
// tracking frequency is valid, calculate required settings and select band
auto amplitude = HW::GetAmplitudeSettings(s.trackingPower, trackingFreq, s.applySourceCorrection, s.trackingGeneratorPort);
// only set the flag here, it is reset at the beginning of each sweep (this makes sure it is set if any of the points are not reached by the TG)
if(amplitude.unlevel) {
HW::SetOutputUnlevel(true);
}
attenuator = amplitude.attenuator;
if(trackingFreq < HW::BandSwitchFrequency) {
Si5351.SetCLK(SiChannel::LowbandSource, trackingFreq, Si5351C::PLL::B, amplitude.lowBandPower);
FPGA::Disable(FPGA::Periphery::SourceChip);
FPGA::Disable(FPGA::Periphery::SourceRF);
trackingLowband = true;
} else {
// Source PLL can not hit all frequencies with high enough accuracy with a single reference frequency.
// Check available reference frequencies for best match
uint8_t bestIndex = 0;
uint32_t smallestDeviation = UINT32_MAX;
for(uint8_t i=0;i<PLLRefFreqsNum;i++) {
Source.SetReference(PLLRefFreqs[i], false, 1, false);
Source.SetFrequency(trackingFreq);
auto actualSource = Source.GetActualFrequency();
uint32_t deviation = (uint32_t) abs(actualSource - trackingFreq);
if(deviation < smallestDeviation) {
smallestDeviation = deviation;
bestIndex = i;
if(deviation < actualRBW / 20) {
// good enough, no need to check any further
break;
}
}
}
if(bestIndex != PLLRefIndex) {
LOG_INFO("Switching ref index (current %d, requested f=%lu%06lu)", PLLRefIndex
,(uint32_t) (trackingFreq / 1000000), (uint32_t)(trackingFreq%1000000));
PLLRefIndex = bestIndex;
setPLLReference();
}
Source.SetFrequency(trackingFreq);
Source.SetPowerOutA(amplitude.highBandPower, true);
FPGA::Enable(FPGA::Periphery::SourceChip);
FPGA::Enable(FPGA::Periphery::SourceRF);
trackingLowband = false;
// selected power potentially changed, update default registers
FPGA::WriteMAX2871Default(Source.GetRegisters());
}
}
}
}
@ -158,7 +197,9 @@ static void StartNextSample() {
// only adjust LO2 PLL if necessary (if the deviation is significantly less than the RBW it does not matter)
if((uint32_t) abs(LO2freq - lastLO2) > actualRBW / 100) {
Si5351.SetPLL(Si5351C::PLL::B, LO2freq*HW::LO2Multiplier, HW::Ref::getSource());
// Si5351.SetPLL(Si5351C::PLL::B, LO2freq*HW::LO2Multiplier, HW::Ref::getSource());
Si5351.SetCLK(SiChannel::Port1LO2, LO2freq, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
Si5351.SetCLK(SiChannel::Port2LO2, LO2freq, Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
lastLO2 = LO2freq;
}
if (s.UseDFT) {
@ -228,6 +269,10 @@ void SA::Setup(Protocol::SpectrumAnalyzerSettings settings) {
// set initial state
pointCnt = 0;
signalIDstep = 0;
trackingFreq = 0;
PLLRefIndex = 0;
setPLLReference();
// enable the required hardware resources
Si5351.Enable(SiChannel::Port1LO2);
Si5351.Enable(SiChannel::Port2LO2);