diff --git a/mc_pd_eval3.m b/mc_pd_eval3.m
index d7e5ae0..5a02dc4 100644
--- a/mc_pd_eval3.m
+++ b/mc_pd_eval3.m
@@ -23,7 +23,9 @@
 ## Author: Jens <jens@orion>
 ## Created: 2020-08-07
 
-function retval = mc_pd_eval3 (phase_lo, freq, slave_oversample)
+function retval = mc_pd_eval3 (phase, freq, slave_oversample)
+
+USE_TRIGON = 0;
 
 Nc = 10;
 Nspc = 25;
@@ -50,8 +52,19 @@ dfreq = freq/slave_oversample;
 omega = 0;
 
 sample_count = slave_oversample;
+
+a = 0.5;
+y(1) = a*cos(2*pi*phase);
+y(2) = a*sin(2*pi*phase);
+
 for n=1:N,
-	phase = mod(phase_lo - 0.5, 1);
+	if USE_TRIGON
+		[phase, y] = process_trigon(y, omega);
+	else
+		phase = process_linear_phase(phase, omega);
+	endif
+	_lo(n) = phase;
+
 	perr = phase_det(phase, x(n));
 	sample_count = sample_count - 1;
 	if sample_count == 0,
@@ -59,18 +72,29 @@ for n=1:N,
 	else
 		perr = 0;
 	end
-	_lo(n) = phase_lo;
+	
 	omega = dfreq - (klag*lag + klead*perr);
-	phase_lo = mod(phase_lo + omega, 1);
 	lag = lag + perr;
 	_perr(n) = perr;
 	_omega(n) = omega;
 end
 
 function perr = phase_det(lo, x)
+	lo = mod(lo - 0.5, 1);
 	perr = mod((lo - x), 1) - 0.5;
 endfunction
 
+function phase_out = process_linear_phase(phase_in, omega)
+	phase_out = mod(phase + omega, 1);
+endfunction
+
+function [phase_out, y] = process_trigon(y, omega)
+	b = 2.0 * sin(pi*omega);
+	y(1) = y(1) - b*y(2);
+	y(2) = y(2) + b*y(1);
+	phase_out = mod(0.5 + 0.5*atan2(y(1), -y(2))/pi, 1);
+endfunction
+
 close all;
 subplot(3, 1, 1)
 plot(1:N, _lo, 1:N, x); legend('Lo', 'x'); grid