isppac81 Lattice Semiconductor Corp., isppac81 Datasheet - Page 9

• Manufacturer Part Number: isppac81
• Description: In-system Programmable Analog Circuit
• Manufacturer: Lattice Semiconductor Corp.

Lattice Semiconductor
Theory of Operation
Reference Configuration
In the specifications table, specific filter configurations are referred to, such as the CC055042 at 17.62kHz. This is
simply a shorthand notation for the classical filter type that includes all the characteristic parameters of the particu-
lar configuration. In this case, the CC refers to complete Chebyshev, or a Chebyshev ripple response in both the
pass and stopbands of the filter. Another common name for this type of filter is the Elliptic family of filters. The next
set of numbers, “05” refers to the order of the filter. In the case of ispPAC81 this will always be fifth order. The next
two digits signify the reflection coefficient (rf), in this case 10%, and has a direct mathematical relationship to the
passband ripple magnitude of the filter, where the passband ripple expressed in dB = 10*Log(1-rf
digits are the passband to stopband attenuation ratio expressed as an angle, in this case 42 degrees or 1.49 (1/
sin((π/180)*42)). This configuration corresponds to the elliptical filter with the ID# 1088 (Fp=17.62kHz;
Fc=17.96kHz) in the filter configuration database utility of PAC-Designer. Because of the almost limitless number of
configurations realizable with ispPAC81, standard test configurations had to be chosen. The Elliptical family was
chosen since it has many parameters that can be easily and directly measured to insure that all the internal circuits
of ispPAC81 are operating correctly.
Figure 1. Simplified ispPAC81 Filter Core Schematic
V OUT
V IN
V IN
20K
Rin
=
+
2(L2 C5 G 3 ) - 2(G 3 L4 C2)
R11 20K
A1
A1
C1
+
V1
+
2(G 4 C5)
-20K
(L2 C1 C3 G 2
R21
20K
R12
G = 1/20K; G/2 = 1/40K; C2 = C231 = C213; C4 = C435; C4/2 = C453
+
-(L2 G C4 2 L4)
- L C C G
2 2 1 4
(
+
- G (L L C C )s
2
( 4 4 C3) - 2(G 4 C4)
-(L2 C4 2 L4 C1) 2(L2 C1 C3 L4 C5) - 2(C2 2 L2 L4 C5)
G
A2
+
(
G 3 L4 C3)
C231
C213
L2
) (
2 4 4 2 4
+
V2
L2 G 2 C3 L4) - (G 2 L4 C4 2
2
+
)
R23
20K
(
+
L2 C1 C3 L4 G) - (C2 2 L2 L4 G) 2(L2 G C3 L4 C5)
2
-20K
+
R32
(
G C L C
(
L2 G 3 C1) 2(G 3 L4 C5) - 2( L2 C4 G 3
+
2 1 4 5
+
+
(
G 4 L4)
((L G C
9
A3
2
+
C3
)
+
+
2
(
2 2 5
G 4 C1)
(
V3
L C G C - C
2
) (
)
+
+
2(G 2 2 L4 C5 C3) - 4(G 2 L4 C5 C2)
G L C ) s
-20K
R34
+
2 4 4
R43
20K
(
2 1
L2 G 4 ) - 2(G 4 C2) s
+
) (
)
A4
2 2 2
2
C453
C435
L4
+
L G
G
V4
) (
4
+
s
ispPAC81 Data Sheet
5
G 3 C1 L4)
R45
20K
2
)
+
s
-40K
3
R54
s
2 G 5
4
+
2
A5
R55
40K
). The final two
(
C5
L2 C3 G 3 ) s 2
V OUT