Phase locked loop with modified loop filter
A loop filter in a modified phase locked loop has a proportional path generating first output signal that is proportional to an input signal and an integral path for generating a second output signal that is an integral of the input signal. An additional functional path generates a third output signal that is a predetermined function of the input signal. The predetermined function is of the form f(s)/g(s), where f and g are polynomial functions. An adder combines the first, second, and third output signals into a common output signal.
1. A modified phase locked loop including a loop filter comprising:
a proportional path generating first output signal that is proportional to an input signal;
an integral path for generating a second output signal that is an integral of the input signal;
an additional functional path for generating a third output signal that is a predetermined function of the input signal, said predetermined function being of the form f(s)/g(s), where f and g are polynomial functions; and
an adder configured to combine said first, second, and third output signals into a common output signal and wherein the loop filter has a transfer function H(s) of the form:
H
(
s
)
=
X
1
+
X
2
s
+
X
3
s
wherein
X 1 =2ξω n
X 2 =ω n 2
X 3 =1
and where ξ is the damping factor, and ω n is the natural frequency of the phase locked loop.
2. A method of modifying a phase locked loop including a loop filter with a proportional path generating first output signal that is proportional to an input signal of the look filter and an integral path for generating a second output signal that is an integral of the input signal, said method comprising adding an additional functional path to generate a third output signal that is a predetermined function of the input signal, said predetermined function being of the form f(s)/g(s), where f and g are polynomial functions, and combining said first, second, and third output signals into a common output signal of the loop filter, and wherein the loop filter has a transfer function H(s) of the form:
H
(
s
)
=
X
1
+
X
2
s
+
X
3
s
wherein
X 1 =2ξω n
X 2 =ω n 2
X 3 =1
and where ξ is the damping factor, and ω n is the natural frequency of the phase locked loop.