Simulates the operation of the phaselocked loop (PLL) in response to an input complex baseband waveform that has an unknown phase and frequency offset.
This node attempts to track the unknown phase of an input complex exponential tone by means of a feedback control system. At steady state, when the PLL has acquired a lock to the input signal, the PLL estimates the offset of the input signal carrier phase and carrier frequency from the reference phase and frequency. The baseband waveform is assumed to consist of a tone at a userspecified nominal carrier phase and frequency, which is used as a reference to the PLL. The PLL is a feedback control system that employs a phase detector, loop filter, and a voltagecontrolled oscillator (VCO) for its operation. The PLL tracks the instantaneous phase and frequency of the input waveform and returns an estimate of the carrier phase and frequency. You can use these estimates to adjust or correct the phase of the input waveform, for example, carrier phase or frequency offset correction in Mary PSK digital communication systems.
baseband waveform
Cluster comprising the I/Q baseband waveform values that represent the complex envelope. The complex envelope is assumed to consist of a tone with a frequency and phase that are to be estimated by the PLL.
t0
The trigger (start) time of the Y array.
Default: 0.0
dt
Time interval between data points in the Y array.
Default: 1.0
Y
The complexvalued timedomain data array. The real and imaginary parts of this complex data array correspond to the inphase (I) and quadraturephase (Q) data, respectively.
Default: empty
VCO carrier frequency
The reference carrier frequency, in Hertz (Hz), which is used by the VCO to track the carrier phase of the input signal.
Default: 0
VCO initial phase
The reference initial carrier phase, in degrees, which is used by the VCO to track the carrier phase of the input signal.
Default: 0
VCO gain
The gain applied to the error signal inside the VCO before generating the estimated initial phase parameter.
Default: 1
error in
Error conditions that occur before this node runs.
The node responds to this input according to standard error behavior.
Default: no error
loop filter forward coefficients
The forward coefficients of the IIR loop filter.
Default: (1.05 0.95)
reset ?
A Boolean that determines whether to clear the internal state of the PLL prior to starting operation.
TRUE 
Clears all state information, and initializes the PLL with the initial phase given in the PLL settings cluster. 
FALSE 
Uses the state information at the end of the previous iteration to initialize the PLL at the beginning of the current iteration. 
Default: TRUE
loop filter reverse coefficients
The reverse coefficients of the IIR loop filter.
Default: (1 1)
VCO phase
The overall phase of the input signal estimated by the PLL, including the effects of any carrier phase and frequency offsets.
phase error
The carrier phase error signal at the phase detector output inside the PLL. You can use this value to estimate the phase difference between the input signal and the regenerated phase at the PLL output. When the PLL locks, phase error values approach zero.
estimated carrier frequency
The actual carrier frequency of the input signal, as estimated by the PLL, accounting for any carrier frequency offset. Use the difference between the estimated carrier frequency and the nominal input carrier frequency to estimate the carrier frequency offset.
estimated initial phase
The actual carrier phase of the input signal, as estimated by the PLL, with respect to the specified nominal carrier phase. Use the difference between the estimated carrier phase and the input nominal carrier phase to estimate the scalar carrier phase offset.
PhaseLocked Loop Elements
The PLL nodes are continuable, meaning that you can successively send a phasecontinuous signal to the node over multiple iterations when reset? is set to FALSE. A PLL contains three basic elements:

Phase detector

IIR loop filter

Voltage controlled oscillator (VCO)
The phase detector block measures the approximate error between the estimated phase and the actual phase of the incoming signal. The IIR loop filter block then filters out any highfrequency noise present in the error signal and helps tracking phase and frequency offset errors. A firstorder lowpass filter block tracks an initial phase offset, but returns a constant phase offset in the presence of a frequency offset. Higherorder filters track both phase and frequency offsets at steady state, as summarized in the following table.
F(s) 
F(z) 
Comments 
1 
1 
(Order I) Tracks frequency error, steady state phase offset 
$1+\frac{a}{s}$ 
$\frac{(0.5a+1)+(0.5a1){z}^{2}}{1{z}^{1}}$ 
(Order II) Tracks phase and frequency error, not offset 
$\frac{s+a}{s+\epsilon}$ 
$M\frac{1\left(\frac{2a}{2+a}\right){z}^{1}}{1\left(\frac{2\epsilon}{2+\epsilon}\right){z}^{1}}$ 
(Order II) Tracks phase and frequency error, not offset 
$1+\frac{a}{s}+\frac{b}{{s}^{2}}$ 
$\frac{(4+2a+b)+(2b8){z}^{1}+(b2a+4){z}^{2}}{4(12{z}^{1}+{z}^{2})}$ 
(Order III) Tracks phase and frequency error, not offset 
Installed By: LabVIEW Communications System Design Suite (introduced in 1.0)
Where This Node Can Run:
Desktop OS: Windows
FPGA: Not supported