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Agilent EEsof EDA PLL's using a Charge Pump, High Divide-by-N Factors, and Decimation before Plotting This document is owned by Agilent Technologies, but is no longer kept current and may contain obsolete or inaccurate references. We regret any inconvenience this may cause. For the latest information on Agilent's line of EEsof electronic design automation (EDA) products and services, please go to: www.agilent.com/find/eesof Application Note AN126E Mar 20, 2001 Phase Locked Loops (PLL) using a Charge Pump, PLL's with High Divide-by-N Factors, and Decimation Before Plotting By Stephen H. Kratzet Introduction PLL Example 1 -- The Charge Pump A spreadsheet approach will be shown for designing a The 1st example is taken directly from a National phase locked loop (PLL) that uses a charge pump. Semiconductor application note (Ref. 1). Figure 1 shows Although the spreadsheet is specific to SystemView by what the PLL looks like in SystemView. To simulate the ELANIX, it may be used for other PLL systems using a 5.0 ma current sources in the charge pump, two step charge pump. In SystemView, PLL's with a high divide- source tokens are used at the input to the charge pump: by-N factor (greater than ~1000) will result in very long +5000 volts and -5000 volts Inside the charge pump, plotting times. In these cases, decimation of the sink data there is a resistor in series with each of the 5000 volt can dramatically speed up the plotting times. inputs. Each of the series resistors is set to 1.0 e6 ohms. Figure 1. A divide by 4,500 PLL with a charge pump, followed by a low pass RC filter. AN126E Mar 20, 2001 SystemView by ELANIX Page 1 of 10 Other parameter values can be used for the current partial solution is to use a limit token from the Function source that have almost no effect on the VCO control library at the output of the RC_Cpump token. Although waveform. A 50.0 volt source with a 10.0 k resistor and the limit token is not used here, its parameters could be set a 5.0 volt source with a 1.0 k resistor each worked fine. as follows: However, there is a difference in each of the Bode plots Input Max (+/- v): 5 for the various voltage/resistor combinations. The -3dB Output Max (+/- v): 5 point for the lowpass cutoff frequency tracks the resistor value. When 5000 volts and a 1.0 Meg resistor are used, Reference Sideband Spur Filter the lowpass -3dB point is moved far away from the