[Discuss-gnuradio] question about advance_loop function in gri_control_loop.cc

[adream]

hello,

the function of advance_loop and update_gain is defined as follow in gri_control_loop.cc

void gri_control_loop::update_gains()

{

  float denom = (1.0 + 2.0*d_damping*d_loop_bw + d_loop_bw*d_loop_bw);

  d_alpha = (4*d_damping*d_loop_bw) / denom;

  d_beta = (4*d_loop_bw*d_loop_bw) / denom;

}

void gri_control_loop::advance_loop(float error)

{

  d_freq = d_freq + d_beta * error;

  d_phase = d_phase + d_freq + d_alpha * error;

}

Is there any paper explains why the d_freq and d_phase is calculated in such equation?

Thanks