150MHz to 170MHz in 25kHz steps using a LMX2306 PLL

Posted on Feb 6, 2014

Using SimPLL`s new PLL Wizard you can design a new PLL with a few clicks of the mouse. We have just designed one that tunes from 150MHz to 170MHz in 25kHz steps using a LMX2306 PLL IC and a MiniCircuits POS300 VCO. and because the LMX2306 and MiniCircuits POS300 are in the libraries, you haven`t had to enter any device data. The PLL has been desig

150MHz to 170MHz in 25kHz steps using a LMX2306 PLL
Click here to download the full size of the above Circuit.

ned with a loop bandwidth of 2. 5kHz and a phase margin of 45degrees. SimPLL predicts the phase noise from the synthesizer. To evaluate which phase detector current setting to use we compared the 250uA setting (red trace) to the 1mA setting (blue trace), both with a loop bandwidth of 2. 5kHz. The difference is due to the larger loop filter resistor in the low current case. Showing the effect of 1nA of DC current at the phase detector. This could be from phase detector leakage, in some cases from loop filter capacitor leakage or VCO varactor diode leakage. Modulation frequency response from modulating the VCO, showing the peaking around the loop bandwidth. Blue trace is with a 45 degree phase margin, red trace has a 60 degree phase margin to reduce peaking. Loop settling is easily observed on the plot of |frequency error|. This shows at a glance that the loop takes about 1. 1ms to lock to within 1kHz and 1. 5ms to lock within 10Hz The VCO phase error is an important parameter in many digital communications systems - here we can see that for the transient plotted above, the VCO takes about 1. 1ms to lock to within 10 degrees of its final phase. SimPLL even provides you with details of the output of the lock detect filter. Shown here in the blue trace is the output from the two time constant analog lock detect filter shown in the schematic, the red trace is the lock detect output using the LMX2306 digital lock detect circuit....

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