请给出输入频率为50Mhz,输出频率为1.6Ghz-2.0Ghz的电荷泵锁相环的行为级建模Verilog-A代码

对于电荷泵锁相环的行为级建模Verilog-A代码，可以参考如下代码：

`include "constants.vams"

module charge_pump_pll (
  input clk,        // 输入时钟
  input reset,      // 复位信号
  input feedback,   // 反馈信号
  output reg out    // 输出信号
);

  // 定义参数
  parameter Fref = 50e6;     // 输入频率
  parameter Fout_min = 1.6e9; // 输出频率最小值
  parameter Fout_max = 2.0e9; // 输出频率最大值
  parameter Kvco = 48e6;     // VCO增益
  parameter C1 = 1e-12;      // 电荷泵电容1
  parameter C2 = 2e-12;      // 电荷泵电容2
  parameter Icp = 1e-6;      // 电荷泵电流

  // 定义局部变量
  real theta, Kp, Ki, Kd, Kf, Kpfd, Kifd, Kdfd;
  real phase_error, phase_error_int, phase_error_diff, phase_error_filt, phase_error_fd_int, phase_error_fd;

  // 定义状态变量
  real Kv, Kp_out, Ki_out, Kd_out, Kf_out, Kpfd_out, Kifd_out, Kdfd_out;
  real vco_freq, vco_phase, charge_pump_out, loop_filter_out, phase_detector_out, phase_error_fd_out;
  real v1, v2, v3, v4, i1, i2, i3, i4, i5, i6, i7, i8, i9;

  // 初始化状态变量
  initial begin
    Kv = Kvco / (2 * PI);
    Kp_out = Kv * C1 * Icp;
    Ki_out = Kv * C1 * C2 * Icp * Icp / (2 * PI);
    Kd_out = Kv * C2 * Icp / (2 * PI);
    Kf_out = 1 / (2 * PI * Fout_min);
    Kpfd_out = Kv * C1 * Icp / (2 * PI);
    Kifd_out = Kv * C1 * C2 * Icp * Icp / (2 * PI);
    Kdfd_out = Kv * C2 * Icp / (2 * PI);
    vco_freq = Fout_min;
  end

  // 定义电荷泵
  assign charge_pump_out = (feedback > 0) ? Icp : -Icp;

  // 定义环路滤波器
  assign loop_filter_out = Kp_out * (v1 - v2) + Ki_out * (v3 - v4);
  assign i1 = loop_filter_out / (Kp_out * C1);
  assign i2 = -charge_pump_out;
  assign i3 = loop_filter_out / (Ki_out * C1 * C2);
  assign i4 = -charge_pump_out;
  assign v1 = i1 * C1;
  assign v2 = i2 * C1;
  assign v3 = i3 * C2;
  assign v4 = i4 * C2;

  // 定义相位检测器
  assign phase_detector_out = feedback * vco_phase;

  // 定义相位误差
  assign phase_error = phase_detector_out / (2 * PI * vco_freq);

  // 定义相位误差积分
  assign i5 = Kpfd_out * phase_error;
  assign i6 = -charge_pump_out;
  assign i7 = Ki_out * phase_error_int;
  assign i8 = -charge_pump_out;
  assign phase_error_int = i5 * C1 + i6 * C1 + i7 * C1 * C2 + i8 * C1 * C2;

  // 定义相位误差微分
  assign i9 = Kdfd_out * phase_error_diff;
  assign phase_error_diff = (2 * PI * Fref) * (phase_error - phase_error_filt);
  assign phase_error_filt = Kf_out * phase_error_diff + (1 - Kf_out) * phase_error_filt;

  // 定义频率调整器
  assign i10 = Kp_out * phase_error_fd;
  assign i11 = -charge_pump_out;
  assign i12 = Ki_out * phase_error_fd_int;
  assign i13 = -charge_pump_out;
  assign phase_error_fd_int = i10 * C1 + i11 * C1 + i12 * C1 * C2 + i13 * C1 * C2;
  assign phase_error_fd = (Fout_max - vco_freq) / vco_freq;

  // 定义VCO
  always @ (posedge clk or posedge reset) begin
    if (reset) begin
      vco_freq <= Fout_min;
      vco_phase <= 0;
    end else begin
      vco_freq <= vco_freq + loop_filter_out;
      vco_phase <= vco_phase + vco_freq * 2 * PI / Fref;
      if (vco_phase > 2 * PI) begin
        vco_phase <= vco_phase - 2 * PI;
        out <= ~out;
      end
    end
  end

endmodule

需要注意的是，此代码仅作为参考，实际情况需要根据具体的电路设计进行修改。