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switch PLL reference to avoid integer spurs

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This commit is contained in:
Jan Käberich 2025-03-03 15:42:14 +01:00
parent 224b2abc5c
commit b133728f1d
1 changed files with 72 additions and 16 deletions
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88
Software/VNA_embedded/Application/VNA.cpp
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@ -50,6 +50,10 @@ static constexpr uint16_t maxPointsBetweenHalts = 40;
static constexpr uint16_t full2portDatapointSize = 66;// See Protocol::VNADatapoint:: static constexpr uint16_t full2portDatapointSize = 66;// See Protocol::VNADatapoint::
static constexpr uint32_t reservedUSBbuffer = (maxPointsBetweenHalts + 2 /*additional buffer*/) * (full2portDatapointSize + 8 /*USB packet overhead*/); static constexpr uint32_t reservedUSBbuffer = (maxPointsBetweenHalts + 2 /*additional buffer*/) * (full2portDatapointSize + 8 /*USB packet overhead*/);
static uint32_t PLLRefFreqs[] = {HW::PLLRef, HW::PLLRef - 1000000};
static constexpr uint8_t PLLRefFreqsNum = sizeof(PLLRefFreqs)/sizeof(PLLRefFreqs[0]);
static uint8_t sourceRefIndex, LO1RefIndex;
using namespace HWHAL; using namespace HWHAL;
static uint64_t getPointFrequency(uint16_t pointNum) { static uint64_t getPointFrequency(uint16_t pointNum) {
@ -71,16 +75,43 @@ static uint64_t getPointFrequency(uint16_t pointNum) {
} }
} }
static void setPLLFrequencies(uint64_t f) { static bool setPLLFrequencies(uint64_t f) {
uint64_t sourceFreq = 0;
uint64_t LOFreq = 0;
if(f > HW::Info.limits_maxFreq) { if(f > HW::Info.limits_maxFreq) {
Source.SetFrequency(f / sourceHarmonic); sourceFreq = f / sourceHarmonic;
LO1.SetFrequency((f + HW::getIF1()) / LOHarmonic); LOFreq = (f + HW::getIF1()) / LOHarmonic;
} else { } else {
if(f >= HW::BandSwitchFrequency) { if(f >= HW::BandSwitchFrequency) {
Source.SetFrequency(f); sourceFreq = f;
} }
LO1.SetFrequency(f + HW::getIF1()); LOFreq = f + HW::getIF1();
} }
if(sourceFreq > 0) {
Source.SetFrequency(sourceFreq);
}
LO1.SetFrequency(LOFreq);
bool needsRefSwitch = false;
if(settings.suppressPeaks) {
// Integer spurs can cause a small peak.
uint32_t sourceDist = Source.DistanceToIntegerSpur();
uint32_t LODist = LO1.DistanceToIntegerSpur();
if((sourceDist > 0) && (sourceDist < 3 * HW::getIF2())) {
LOG_INFO("Source spur at %lu: %lu", (uint32_t) f, sourceDist);
sourceRefIndex = !sourceRefIndex;
Source.SetReference(PLLRefFreqs[sourceRefIndex], false, 1, false);
Source.SetFrequency(sourceFreq);
needsRefSwitch = true;
}
if((LODist > 0) && (LODist < 3 * HW::getIF2())) {
LOG_INFO("LO spur at %lu", (uint32_t) f);
LO1RefIndex = !LO1RefIndex;
LO1.SetReference(PLLRefFreqs[LO1RefIndex], false, 1, false);
LO1.SetFrequency(LOFreq);
needsRefSwitch = true;
}
}
return needsRefSwitch;
} }
static bool needs2LOshift(uint64_t f, uint32_t current2LO, uint32_t IFBW, uint32_t *new2LO) { static bool needs2LOshift(uint64_t f, uint32_t current2LO, uint32_t IFBW, uint32_t *new2LO) {
@ -108,11 +139,17 @@ static bool needs2LOshift(uint64_t f, uint32_t current2LO, uint32_t IFBW, uint32
} }
bool VNA::Setup(Protocol::SweepSettings s) { bool VNA::Setup(Protocol::SweepSettings s) {
// Abort possible active sweep first
VNA::Stop(); VNA::Stop();
vTaskDelay(5); vTaskDelay(5);
data.clear(); data.clear();
HW::SetMode(HW::Mode::VNA); HW::SetMode(HW::Mode::VNA);
// Abort possible active sweep first
sourceRefIndex = 0;
LO1RefIndex = 0;
Source.SetReference(PLLRefFreqs[sourceRefIndex], false, 1, false);
LO1.SetReference(PLLRefFreqs[LO1RefIndex], false, 1, false);
FPGA::SetMode(FPGA::Mode::FPGA); FPGA::SetMode(FPGA::Mode::FPGA);
FPGA::WriteRegister(FPGA::Reg::ADCPrescaler, HW::getADCPrescaler()); FPGA::WriteRegister(FPGA::Reg::ADCPrescaler, HW::getADCPrescaler());
FPGA::WriteRegister(FPGA::Reg::PhaseIncrement, HW::getDFTPhaseInc()); FPGA::WriteRegister(FPGA::Reg::PhaseIncrement, HW::getDFTPhaseInc());
@ -199,7 +236,9 @@ bool VNA::Setup(Protocol::SweepSettings s) {
} }
// SetFrequency only manipulates the register content in RAM, no SPI communication is done. // SetFrequency only manipulates the register content in RAM, no SPI communication is done.
// No mode-switch of FPGA necessary here. // No mode-switch of FPGA necessary here.
setPLLFrequencies(freq); if(setPLLFrequencies(freq)) {
needs_halt = true;
}
uint32_t new_LO2; uint32_t new_LO2;
auto needs_shift = needs2LOshift(freq, last_LO2, actualBandwidth, &new_LO2); auto needs_shift = needs2LOshift(freq, last_LO2, actualBandwidth, &new_LO2);
if(needs_shift) { if(needs_shift) {
@ -249,6 +288,11 @@ bool VNA::Setup(Protocol::SweepSettings s) {
FPGA::Samples::SPPRegister, needs_halt); FPGA::Samples::SPPRegister, needs_halt);
last_lowband = lowband; last_lowband = lowband;
} }
// reset a possibly changed PLL reference index
sourceRefIndex = 0;
LO1RefIndex = 0;
Source.SetReference(PLLRefFreqs[sourceRefIndex], false, 1, false);
LO1.SetReference(PLLRefFreqs[LO1RefIndex], false, 1, false);
// revert clk configuration to previous value (might have been changed in sweep calculation) // revert clk configuration to previous value (might have been changed in sweep calculation)
Si5351.SetCLK(SiChannel::RefLO2, HW::getIF1() - HW::getIF2(), Si5351C::PLL::B, Si5351C::DriveStrength::mA2); Si5351.SetCLK(SiChannel::RefLO2, HW::getIF1() - HW::getIF2(), Si5351C::PLL::B, Si5351C::DriveStrength::mA2);
Si5351.ResetPLL(Si5351C::PLL::B); Si5351.ResetPLL(Si5351C::PLL::B);
@ -438,10 +482,30 @@ void VNA::SweepHalted() {
Si5351.Disable(SiChannel::LowbandSource); Si5351.Disable(SiChannel::LowbandSource);
FPGA::Enable(FPGA::Periphery::SourceRF); FPGA::Enable(FPGA::Periphery::SourceRF);
} }
if (pointCnt == 0 && settings.suppressPeaks) {
sourceRefIndex = 0;
LO1RefIndex = 0;
Source.SetReference(PLLRefFreqs[sourceRefIndex], false, 1, false);
LO1.SetReference(PLLRefFreqs[LO1RefIndex], false, 1, false);
// update PLL reference frequencies
Si5351.SetCLK(SiChannel::Source, PLLRefFreqs[sourceRefIndex], Si5351C::PLL::A, Si5351C::DriveStrength::mA8);
Si5351.SetCLK(SiChannel::LO1, PLLRefFreqs[LO1RefIndex], Si5351C::PLL::A, Si5351C::DriveStrength::mA8);
last_LO2 = HW::getIF1() - HW::getIF2();
Si5351.SetPLL(Si5351C::PLL::B, last_LO2*HW::LO2Multiplier, HW::Ref::getSource());
Si5351.ResetPLL(Si5351C::PLL::B);
Si5351.WaitForLock(Si5351C::PLL::B, 10);
HAL_Delay(2);
}
if(settings.suppressPeaks) { if(settings.suppressPeaks) {
// does not actually change PLL settings, just calculates the register values and // does not actually change PLL settings, just calculates the register values and
// is required to determine the need for a 2.LO shift // is required to determine the need for a 2.LO shift
setPLLFrequencies(frequency); if(setPLLFrequencies(frequency)) {
// update PLL reference frequencies
Si5351.SetCLK(SiChannel::Source, PLLRefFreqs[sourceRefIndex], Si5351C::PLL::A, Si5351C::DriveStrength::mA8);
Si5351.SetCLK(SiChannel::LO1, PLLRefFreqs[LO1RefIndex], Si5351C::PLL::A, Si5351C::DriveStrength::mA8);
}
if(needs2LOshift(frequency, last_LO2, actualBandwidth, &last_LO2)) { if(needs2LOshift(frequency, last_LO2, actualBandwidth, &last_LO2)) {
Si5351.SetPLL(Si5351C::PLL::B, last_LO2*HW::LO2Multiplier, HW::Ref::getSource()); Si5351.SetPLL(Si5351C::PLL::B, last_LO2*HW::LO2Multiplier, HW::Ref::getSource());
Si5351.ResetPLL(Si5351C::PLL::B); Si5351.ResetPLL(Si5351C::PLL::B);
@ -451,14 +515,6 @@ void VNA::SweepHalted() {
} }
} }
if (pointCnt == 0) {
last_LO2 = HW::getIF1() - HW::getIF2();
Si5351.SetPLL(Si5351C::PLL::B, last_LO2*HW::LO2Multiplier, HW::Ref::getSource());
Si5351.ResetPLL(Si5351C::PLL::B);
Si5351.WaitForLock(Si5351C::PLL::B, 10);
HAL_Delay(2);
}
if(adcShiftRequired) { if(adcShiftRequired) {
FPGA::WriteRegister(FPGA::Reg::ADCPrescaler, alternativePrescaler); FPGA::WriteRegister(FPGA::Reg::ADCPrescaler, alternativePrescaler);
FPGA::WriteRegister(FPGA::Reg::PhaseIncrement, alternativePhaseInc); FPGA::WriteRegister(FPGA::Reg::PhaseIncrement, alternativePhaseInc);