What do you mean with a time interval? Is there a delay between the two signals or a phase difference? It is unclear to me what the circuit is supposed to do. Would it be possible to explain or to point to a site where such a function is explained.

Marq

I would do something like this:

Code:

module time_diff_amp (z, y, a, b);
input a, b;
output z, y;
electrical z, y, a, b;

parameter real thresh = 0.5;
parameter real tgain = 3.0;
parameter real td = 10p;
parameter real tr = 20p;

real out, last_cross_a, last_cross_b, delta_t;
integer sign_t;

analog begin

  last_cross_a = last_crossing(V(a) - thresh, +1);
  last_cross_b = last_crossing(V(b) - thresh, +1);

  @(cross(V(a) - thresh, -1) or
	cross(V(b) - thresh, -1)) begin
    last_cross_a = 0;
    last_cross_b = 0;
    out = 0;
  end

  @(cross(V(a) - thresh, +1))
    if (last_cross_a > 0 && last_cross_b > 0) begin
	delta_t = tgain * abs(last_cross_a - last_cross_b)
	sign_t = (last_cross_a >= last_cross_b);
	out = 1;
    end

  @(cross(V(b) - thresh, +1))
    if (last_cross_a > 0 && last_cross_b > 0) begin
	delta_t = tgain * abs(last_cross_a - last_cross_b);
	sign_t = (last_cross_a >= last_cross_b);
	out = 1;
    end

  V(z) <+ transition(out, td + sign_t *delta_t, tr);
  V(y) <+ transition(out, td + (1 - sign_t) *delta_t, tr);

end

endmodule // time_diff_amp