th7301 ETC-unknow, th7301 Datasheet - Page 5

• Manufacturer Part Number: th7301
• Description: Dual-channel Programmable Low-pass Filter
• Manufacturer: ETC-unknow

TH7301 Dual-Channel Programmable Low-Pass Filter
Definition of
Terms
Frequency
Setting
Gain Setting
f
f
f
A
To maintain frequency resolution at low frequen-
cies a companding law is applied to the fre-
quency code. The frequency range is selected as
one of the five octaves in the total filter range
controlled by bits FC(2...0). Each octave is divided
linearly into 128 equally sized steps decoded by
bits FS(6...0). This frequency range is for an
external resistor value of 4.5 k
RDAC and VEE. The range is designed to
guarantee 0.8 MHz to 22.4 MHz cutoff range,
taking process variations in top account without
the need to change this external resistor. If there
is a need to fine tune this frequency range for any
reason, it may be re-centered by selecting a
suitably valued external resistor.
The 128 steps within each octave are decoded by
FS(6...0). The according control mechanism
applies identically to all octaves refering to the
appropriate step sizes of each octave, as shown
in the tables and the example below.
Example:
FC(2...0) = 000
(frequency range 0.8 ... 1.5937 MHz,
Step size = 6.25 kHz)
FS(6...0) = 0000011
f
The gain control bits AC(5...0) are decoded to
select a voltage gain between -3 dB and 20.5 dB
in 0.5 dB steps. The gain control is divided into 8
steps controlled by AC(2...0) with additive step
sizes of 0.5 dB decoded by AC(5...3).
For example, to set the gain to 16 dB
AC(5...0) = 011001.
The table below shows the gain setting.
cset
c
step
cset
v
= 0.81875 MHz
-
-
-
-
cutoff frequency setting
cutoff frequency (-3dB bandwidth)
step size
voltage gain
between pin
settings.
The tables below show the selectable frequency
AC(2...0)
0000000
0000001
0000010
0000011
1111111
(6...0)
(2..0)
000
001
010
011
100
101
110
111
000
001
010
011
1xx
FC
FS
.
.
.
Gain (dB)
fmin ... fmax (MHz)
Frequency range
Step N
18
15
12
-3
9
6
3
0
127
0.8 ... 1.5937
1.6 ... 3.1875
3.2 ... 6.375
6.4 ... 12.75
12.8 ... 25.5
0
1
2
3
.
.
.
fcset = fmin + 127*fstep
fcset = fmin + N*fstep
fcset = fmin + 2*fstep
fcset = fmin + 3*fstep
AC(5...3)
Cutoff Frequency
fcset = fmin + fstep
000
001
010
011
100
101
110
111
fcset = fmin
(MHz)
fstep (kHz)
.
.
.
Step size
Gain (dB)
12.5
6.25
100
25
50
2.5
2.0
1.5
1.0
0.5
0.0
0.0
0.0
5