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

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 intended 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

control_loop() [1/2]

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

inline

control_loop() [2/2]

gr::blocks::control_loop::control_loop	(	float	loop_bw,
		float	max_freq,
		float	min_freq
	)

~control_loop()

virtual gr::blocks::control_loop::~control_loop ( )

virtual

Member Function Documentation

advance_loop()

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

inline

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

frequency_limit()

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

inline

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.

get_alpha()

float gr::blocks::control_loop::get_alpha

(

)

const

Returns the loop gain alpha.

get_beta()

float gr::blocks::control_loop::get_beta

(

)

const

Returns the loop gain beta.

get_damping_factor()

float gr::blocks::control_loop::get_damping_factor

(

)

const

Returns the loop damping factor.

get_frequency()

float gr::blocks::control_loop::get_frequency

(

)

const

Get the control loop's frequency estimate.

get_loop_bandwidth()

float gr::blocks::control_loop::get_loop_bandwidth

(

)

const

Returns the loop bandwidth.

get_max_freq()

float gr::blocks::control_loop::get_max_freq

(

)

const

Get the control loop's maximum frequency.

get_min_freq()

float gr::blocks::control_loop::get_min_freq

(

)

const

Get the control loop's minimum frequency.

get_phase()

float gr::blocks::control_loop::get_phase

(

)

const

Get the control loop's phase estimate.

phase_wrap()

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

inline

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.

References GR_M_PI.

set_alpha()

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

set_beta()

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

set_damping_factor()

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

set_frequency()

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

set_loop_bandwidth()

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

set_max_freq()

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

set_min_freq()

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

set_phase()

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

update_gains()

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

d_alpha

float gr::blocks::control_loop::d_alpha

protected

d_beta

float gr::blocks::control_loop::d_beta

protected

d_damping

float gr::blocks::control_loop::d_damping

protected

d_freq

float gr::blocks::control_loop::d_freq

protected

d_loop_bw

float gr::blocks::control_loop::d_loop_bw

protected

d_max_freq

float gr::blocks::control_loop::d_max_freq

protected

d_min_freq

float gr::blocks::control_loop::d_min_freq

protected

d_phase

float gr::blocks::control_loop::d_phase

protected

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

• control_loop.h