spll.rar_spll

function [pd_out,lfvect,uf,vco_phase, vco_out] = spll(sigin, Fs, PD_GAIN,lf_Gain0,lf_Gain1,vco_fc,VCO_GAIN,VCO_AMP) % % % SPLL() - Implements a software phase-locked loop. % % % % Inputs: % % sigin - signal input vector % % Fs - sampling frequency % % PD_GAIN - gain of the phase detector Volts/rad % % lf_Gain0 - gain of the Direct Path of the loop filter % % lf_Gain1 - gain of the Integral Path of the loop filter % % (set to 1.0 in test program. Not really needed) % % vco_fc - center frequency of the vco % % VCO_GAIN - gain of the VCO in rad/(Volts-sec) % % VCO_AMP - amplitude of the VCO % % % % Outputs: % % pd_out - output of the phase detector % % intvect - output of the integrator in vector format % % loop_out - output of the loop filter % % vco_phase - VCO phase history % % vco_out - output of the VCO % %-------------------------------------------------------------------------% Ts = 1/Fs; % sampling period % N = length(sigin); % number of samples % t = [0:Ts:(N*Ts)-Ts]; % time index for samples % pd_out = zeros(N,1); % phase detector output % vco_phase = zeros(N,1); % VCO output % uf = zeros(1,N); lfvect = zeros(1,N); % The low pass filter used in this phase-locked loop is a Butterworth % % 1st order IIR filter. This filter was designed using Matlab's FDATOOL. % % The coefficients are: Fs = 40 kHz, Fcutoff = 1000 Hz. Pole = a1 and % % a Zero = -1. % b0 = 0.0729596572; b1 = 0.0729596572; a1 = -0.8540806854; % MAIN LOOP % vco_out(1) = VCO_AMP * cos(vco_phase(1)); % initial VCO output % pd_out(1) = PD_GAIN * sigin(1) * vco_out(1); % initial phase det out % uf(1) = lf_Gain0*(b0*pd_out(1) + b1*0 - a1*0); lfsum = 0; for n = 2:N % There are various ways to compute the next VCO phase. One way is to % % create a time index nT such that we compute w*(nT), i.e. w*0T, w*1T, % % w*2T, etc. Another way is to compute w*T and just add that value % % each time keeping a running total. The end result is the same. % % The TOTAL phase is a running summation of both the frequency term & % % the phase term. % % Another issue for the successful operation of a PLL is the VCO_GAIN. % % This gain must account for the sampling time interval. Because this % % time multiplies the output of the LFP the numerical value can be % % very small. For example, at 40 kHz sampling, T = 1/40000 = 25e-6. If % % the VCO_GAIN is not large enough this phase term will have no % % noticable affect. A good start is to make the VCO_GAIN equal to the % % sampling frequency. % % wc*t k*uf*T % vco_phase_change = (2*pi*vco_fc*Ts) + VCO_GAIN*uf(n-1)*Ts; vco_phase(n) = vco_phase(n-1) + vco_phase_change; % To insure that the phase term does not grow to infinity addition is % % performed modulo 2*pi. % if(vco_phase(n) > 2*pi) vco_phase(n) = vco_phase(n) - 2*pi; end; vco_out(n) = VCO_AMP * cos(vco_phase(n)); % PHASE DETECTOR % pd_out(n) = PD_GAIN * (sigin(n) * vco_out(n)); % LOW PASS FILTER DIFFERENCE EQ: y(n) = b0*x(n)+b1*x(n-1) - a1*y(n-1) % uf(n) = lf_Gain0*(b0*pd_out(n) + b1*pd_out(n-1) - a1*uf(n-1)); uf(n) = uf(n) * lf_Gain1; % INTEGRATOR. This keeps a running summation of the ouput of the LPF. % lfsum = lfsum + uf(n); lfvect(n) = lfsum; % !!! FOR TESTING !!! % end;