caiyu/LibreVNA
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

remove rise/fall time restriction

Browse Source
This commit is contained in:
Jan Käberich 2022-10-26 10:52:50 +02:00
parent 2dd4edfae6
commit 2357052c95
1 changed files with 47 additions and 47 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

94
Software/PC_Application/LibreVNA-GUI/Traces/eyediagramplot.cpp
View File

@ -778,14 +778,6 @@ void EyeThread::run()
eye.setStatus("Data rate too low");
continue;
}
if(eye.risetime > 0.3 * 1.0 / eye.datarate) {
eye.setStatus("Rise time too high");
continue;
}
if(eye.falltime > 0.3 * 1.0 / eye.datarate) {
eye.setStatus("Fall time too high");
continue;
}
if(eye.jitter > 0.3 * 1.0 / eye.datarate) {
eye.setStatus("Jitter too high");
continue;
@ -898,52 +890,60 @@ void EyeThread::run()
double time = (i+eyeXshift)*timestep;
double voltage;
if(time >= transitionTime) {
// currently within a bit transition
double edgeTime = 0;
double expTimeConstant;
if(currentSignal < nextSignal) {
edgeTime = eye.risetime;
} else if(currentSignal > nextSignal) {
edgeTime = eye.falltime;
}
if(eye.linearEdge) {
// edge is modeled as linear rise/fall
// increase slightly to account for typical 10/90% fall/rise time
edgeTime *= 1.25;
} else {
// edge is modeled as exponential rise/fall. Adjust time constant to match
// selected rise/fall time (with 10-90% signal rise/fall within specified time)
expTimeConstant = edgeTime / 2.197224577;
edgeTime = 6 * expTimeConstant; // after six time constants, 99.7% of signal movement has happened
}
if(time >= transitionTime + edgeTime) {
// bit transition settled
voltage = levelToVoltage(nextSignal);
// move on to the next bit
currentSignal = nextSignal;
nextSignal = getNextLevel();
transitionTime = bitcnt * 1.0 / eye.datarate + dist_jitter(mt_jitter);
bitcnt++;
} else {
// still within rise or fall time
double timeSinceEdge = time - transitionTime;
double from = levelToVoltage(currentSignal);
double to = levelToVoltage(nextSignal);
if(eye.linearEdge) {
double edgeRatio = timeSinceEdge / edgeTime;
voltage = from * (1.0 - edgeRatio) + to * edgeRatio;
} else {
voltage = from + (1.0 - exp(-timeSinceEdge/expTimeConstant)) * (to - from);
}
}
// last transition is over,
// schedule the next transition
voltage = levelToVoltage(nextSignal);
// move on to the next bit
currentSignal = nextSignal;
nextSignal = getNextLevel();
transitionTime = bitcnt * 1.0 / eye.datarate + dist_jitter(mt_jitter);
bitcnt++;
} else {
// still before the next edge
voltage = levelToVoltage(currentSignal);
}
voltage += dist_noise(mt_noise);
inVec[i] = voltage;
}
// add fall/rise time
for(unsigned int i=1;i<inVec.size();i++) {
double last = inVec[i-1].real();
double next = inVec[i].real();
if(last == next) {
// no change, nothing to do
continue;
}
if(eye.linearEdge) {
if(next > last) {
// rising edge
double max_rise = timestep / (eye.risetime * 1.25);
if(next - last > max_rise) {
next = last + max_rise;
}
} else {
// falling edge
double max_fall = timestep / (eye.falltime * 1.25);
if(next - last < -max_fall) {
next = last - max_fall;
}
}
} else {
// exponential edge
// edge is modeled as exponential rise/fall. Adjust time constant to match
// selected rise/fall time (with 10-90% signal rise/fall within specified time)
auto expTimeConstant = (next > last ? eye.risetime : eye.falltime) / 2.197224577;
if(expTimeConstant > 0) {
next = last + (1.0 - exp(-timestep/expTimeConstant)) * (next - last);
}
}
inVec[i] = next;
}
// add noise
for(auto &v : inVec) {
v += dist_noise(mt_noise);
}
// input voltage vector fully assembled
qDebug() << "Eye calculation: input data generated";