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源代碼在單個(gè)文件中預(yù)先提供，并對(duì)其操作進(jìn)行了完整描述。 編譯后，程序?qū)⑦\(yùn)行鎖相環(huán)的模擬，生成一個(gè)數(shù)據(jù)文件，該文件可以使用 Gnuplot 或 Octave 繪制。
- // simulate a phase-locked loop
- #include <stdio.h>
- #include <stdlib.h>
- #include <complex.h>
- #include <math.h>
- int main() {
- // parameters
- float phase_offset = 0.00f; // carrier phase offset
- float frequency_offset = 0.30f; // carrier frequency offset
- float wn = 0.01f; // pll bandwidth
- float zeta = 0.707f; // pll damping factor
- float K = 1000; // pll loop gain
- unsigned int n = 400; // number of samples
- // generate loop filter parameters (active PI design)
- float t1 = K/(wn*wn); // tau_1
- float t2 = 2*zeta/wn; // tau_2
- // feed-forward coefficients (numerator)
- float b0 = (4*K/t1)*(1.+t2/2.0f);
- float b1 = (8*K/t1);
- float b2 = (4*K/t1)*(1.-t2/2.0f);
- // feed-back coefficients (denominator)
- // a0 = 1.0 is implied
- float a1 = -2.0f;
- float a2 = 1.0f;
- // print filter coefficients (as comments)
- printf("# b = [b0:%12.8f, b1:%12.8f, b2:%12.8f]\n", b0, b1, b2);
- printf("# a = [a0:%12.8f, a1:%12.8f, a2:%12.8f]\n", 1., a1, a2);
- // filter buffer
- float v0=0.0f, v1=0.0f, v2=0.0f;
-
- // initialize states
- float phi = phase_offset; // input signal's initial phase
- float phi_hat = 0.0f; // PLL's initial phase
-
- // run basic simulation
- unsigned int i;
- float complex x, y;
- printf("# %6s %12s %12s %12s %12s %12s\n",
- "index", "real(x)", "imag(x)", "real(y)", "imag(y)", "error");
- for (i=0; i<n; i++) {
- // compute input sinusoid and update phase
- x = cosf(phi) + _Complex_I*sinf(phi);
- phi += frequency_offset;
- // compute PLL output from phase estimate
- y = cosf(phi_hat) + _Complex_I*sinf(phi_hat);
- // compute error estimate
- float delta_phi = cargf( x * conjf(y) );
- // print results to standard output
- printf(" %6u %12.8f %12.8f %12.8f %12.8f %12.8f\n",
- i, crealf(x), cimagf(x), crealf(y), cimagf(y), delta_phi);
- // push result through loop filter, updating phase estimate
- v2 = v1; // shift center register to upper register
- v1 = v0; // shift lower register to center register
- v0 = delta_phi - v1*a1 - v2*a2; // compute new lower register
- // compute new output
- phi_hat = v0*b0 + v1*b1 + v2*b2;
- }
- return 0;
- }
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