SELECTED RF BLOCKS IN VHDL-AMS
159
The main characteristics of the lowpass filter are as follows:
The filter gain is measured at zero frequency
10
0
10
gain
out
in
R
a
R
The grade n of filter, which is the exponent of the highest power of S in
H(S) and determines the range of the transition band as well as the
attenuation in the stopband.
Note: In our implementation the grade n of the filter is limited to 6, since
a more general model using the GENERATE construct of VHDL-AMS is
not yet supported by the simulator.
Coefficients of the transition function H(S) are for even values of grade n
(2
1)
2 cos
,
1,
1,...,
2
2
i
i
i
n
a
b
i
n
and for odd values of grade n
1
1
(
1)
1,
2 cos
,
1
0,
1,
2,...,
2
i
i
i
a
a
n
n
b
b
i
The cut-off frequency f
g
(or 3dB frequency) is measured where the gain
drops to
0
2
a
Input and output impedances are modeled as ohmic resistances. Typical
values of a matched system are:
50
in
out
R
R
Additional characteristics, that were not modeled here, include second
order effects such as temperature and power supply dependency of the filter
characteristic, and power consumption.
Summary :
Coefficients of the transition function H(S) are for even values of grade n (2 1) 2 cos , 1, 1,..., 2 2 i i i n a b i n and for odd values of grade n 1 1 ( 1) 1, 2 cos , 1 0, 1, 2,..., 2 i i i a a n n b b i The cut-off frequency f g (or 3dB frequency) is measured where the gain drops to 0 2 a Input and output impedances are modeled as ohmic resistances.
Tags :
filter,grade,power,alues,frequency,gain,out,cos,modeled,characteristics,transition,hdlams,measured