GNU Radio Manual and C++ API Reference  3.7.9.2
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gr::blocks::control_loop Class Reference

A second-order control loop implementation class. More...

#include <gnuradio/blocks/control_loop.h>

Public Member Functions

 control_loop (void)
 
 control_loop (float loop_bw, float max_freq, float min_freq)
 
virtual ~control_loop ()
 
void update_gains ()
 Update the system gains from the loop bandwidth and damping factor. More...
 
void advance_loop (float error)
 Advance the control loop based on the current gain settings and the inputted error signal. More...
 
void phase_wrap ()
 Keep the phase between -2pi and 2pi. More...
 
void frequency_limit ()
 Keep the frequency between d_min_freq and d_max_freq. More...
 
virtual void set_loop_bandwidth (float bw)
 Set the loop bandwidth. More...
 
void set_damping_factor (float df)
 Set the loop damping factor. More...
 
void set_alpha (float alpha)
 Set the loop gain alpha. More...
 
void set_beta (float beta)
 Set the loop gain beta. More...
 
void set_frequency (float freq)
 Set the control loop's frequency. More...
 
void set_phase (float phase)
 Set the control loop's phase. More...
 
void set_max_freq (float freq)
 Set the control loop's maximum frequency. More...
 
void set_min_freq (float freq)
 Set the control loop's minimum frequency. More...
 
float get_loop_bandwidth () const
 Returns the loop bandwidth. More...
 
float get_damping_factor () const
 Returns the loop damping factor. More...
 
float get_alpha () const
 Returns the loop gain alpha. More...
 
float get_beta () const
 Returns the loop gain beta. More...
 
float get_frequency () const
 Get the control loop's frequency estimate. More...
 
float get_phase () const
 Get the control loop's phase estimate. More...
 
float get_max_freq () const
 Get the control loop's maximum frequency. More...
 
float get_min_freq () const
 Get the control loop's minimum frequency. More...
 

Protected Attributes

float d_phase
 
float d_freq
 
float d_max_freq
 
float d_min_freq
 
float d_damping
 
float d_loop_bw
 
float d_alpha
 
float d_beta
 

Detailed Description

A second-order control loop implementation class.

This class implements a second order control loop and is inteded to act as a parent class to blocks which need a control loop (e.g., gr::digital::costas_loop_cc, gr::analog::pll_refout_cc, etc.). It takes in a loop bandwidth as well as a max and min frequency and provides the functions that control the update of the loop.

The loop works of alpha and beta gains. These gains are calculated using the input loop bandwidth and a pre-set damping factor. The damping factor can be changed using the set_damping_factor after the block is constructed. The alpha and beta values can be set using their respective set_alpha or set_beta functions if very precise control over these is required.

The class tracks both phase and frequency of a signal based on an error signal. The error calculation is unique for each algorithm and is calculated externally and passed to the advance_loop function, which uses this to update its phase and frequency estimates.

This class also provides the functions phase_wrap and frequency_limit to easily keep the phase and frequency estimates within our set bounds (phase_wrap keeps it within +/-2pi).

Constructor & Destructor Documentation

gr::blocks::control_loop::control_loop ( void  )
inline
gr::blocks::control_loop::control_loop ( float  loop_bw,
float  max_freq,
float  min_freq 
)
virtual gr::blocks::control_loop::~control_loop ( )
virtual

Member Function Documentation

void gr::blocks::control_loop::advance_loop ( float  error)

Advance the control loop based on the current gain settings and the inputted error signal.

void gr::blocks::control_loop::frequency_limit ( )

Keep the frequency between d_min_freq and d_max_freq.

This function keeps the frequency between d_min_freq and d_max_freq. If the frequency is greater than d_max_freq, it is set to d_max_freq. If the frequency is less than d_min_freq, it is set to d_min_freq.

This function should be called after advance_loop to keep the frequency in the specified region. It is set as a separate method in case another way is desired as this is fairly heavy-handed.

float gr::blocks::control_loop::get_alpha ( ) const

Returns the loop gain alpha.

float gr::blocks::control_loop::get_beta ( ) const

Returns the loop gain beta.

float gr::blocks::control_loop::get_damping_factor ( ) const

Returns the loop damping factor.

float gr::blocks::control_loop::get_frequency ( ) const

Get the control loop's frequency estimate.

float gr::blocks::control_loop::get_loop_bandwidth ( ) const

Returns the loop bandwidth.

float gr::blocks::control_loop::get_max_freq ( ) const

Get the control loop's maximum frequency.

float gr::blocks::control_loop::get_min_freq ( ) const

Get the control loop's minimum frequency.

float gr::blocks::control_loop::get_phase ( ) const

Get the control loop's phase estimate.

void gr::blocks::control_loop::phase_wrap ( )

Keep the phase between -2pi and 2pi.

This function keeps the phase between -2pi and 2pi. If the phase is greater than 2pi by d, it wraps around to be -2pi+d; similarly if it is less than -2pi by d, it wraps around to 2pi-d.

This function should be called after advance_loop to keep the phase in a good operating region. It is set as a separate method in case another way is desired as this is fairly heavy-handed.

void gr::blocks::control_loop::set_alpha ( float  alpha)

Set the loop gain alpha.

Sets the loop filter's alpha gain parameter.

This value should really only be set by adjusting the loop bandwidth and damping factor.

Parameters
alpha(float) new alpha gain
void gr::blocks::control_loop::set_beta ( float  beta)

Set the loop gain beta.

Sets the loop filter's beta gain parameter.

This value should really only be set by adjusting the loop bandwidth and damping factor.

Parameters
beta(float) new beta gain
void gr::blocks::control_loop::set_damping_factor ( float  df)

Set the loop damping factor.

Set the loop filter's damping factor to df. The damping factor should be sqrt(2)/2.0 for critically damped systems. Set it to anything else only if you know what you are doing. It must be a number between 0 and 1.

When a new damping factor is set, the gains, alpha and beta, of the loop are recalculated by a call to update_gains().

Parameters
df(float) new damping factor
void gr::blocks::control_loop::set_frequency ( float  freq)

Set the control loop's frequency.

Sets the control loop's frequency. While this is normally updated by the inner loop of the algorithm, it could be useful to manually initialize, set, or reset this under certain circumstances.

Parameters
freq(float) new frequency
virtual void gr::blocks::control_loop::set_loop_bandwidth ( float  bw)
virtual

Set the loop bandwidth.

Set the loop filter's bandwidth to bw. This should be between 2*pi/200 and 2*pi/100 (in rads/samp). It must also be a positive number.

When a new damping factor is set, the gains, alpha and beta, of the loop are recalculated by a call to update_gains().

Parameters
bw(float) new bandwidth

Reimplemented in gr::analog::pll_carriertracking_cc, and gr::analog::pll_freqdet_cf.

void gr::blocks::control_loop::set_max_freq ( float  freq)

Set the control loop's maximum frequency.

Set the maximum frequency the control loop can track.

Parameters
freq(float) new max frequency
void gr::blocks::control_loop::set_min_freq ( float  freq)

Set the control loop's minimum frequency.

Set the minimum frequency the control loop can track.

Parameters
freq(float) new min frequency
void gr::blocks::control_loop::set_phase ( float  phase)

Set the control loop's phase.

Sets the control loop's phase. While this is normally updated by the inner loop of the algorithm, it could be useful to manually initialize, set, or reset this under certain circumstances.

Parameters
phase(float) new phase
void gr::blocks::control_loop::update_gains ( )

Update the system gains from the loop bandwidth and damping factor.

This function updates the system gains based on the loop bandwidth and damping factor of the system. These two factors can be set separately through their own set functions.

Member Data Documentation

float gr::blocks::control_loop::d_alpha
protected
float gr::blocks::control_loop::d_beta
protected
float gr::blocks::control_loop::d_damping
protected
float gr::blocks::control_loop::d_freq
protected
float gr::blocks::control_loop::d_loop_bw
protected
float gr::blocks::control_loop::d_max_freq
protected
float gr::blocks::control_loop::d_min_freq
protected
float gr::blocks::control_loop::d_phase
protected

The documentation for this class was generated from the following file: