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PDF TH7301 Data sheet ( Hoja de datos )
| Número de pieza | TH7301 | |
| Descripción | Dual-Channel Programmable Low-Pass Filter | |
| Fabricantes | Thesys | |
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TH7301
Dual-Channel Programmable
Low-Pass Filter
Description
The device incorporates two matching 4th-order
Butterworth filters with voltage gain control to
perform low-pass filtering on quadrature demo-
dulated signals. The cutoff frequency and inband
gain are programmable via a standard 3-wire
interface. The cutoff frequency can be set between
0.8 MHz and 22.4 MHz and the inband voltage
gain can be set between -3 dB and 20 dB. The
cutoff frequency value is determined via a 10-bit
control word, with smaller step sizes in the lower
portion of the cutoff frequency range. The device
contains an on-chip oscillator to adjust the cutoff
frequency. Maintaining amplifiers configure the
Butterworth filter as the phase shift component of
the oscillator. The frequency of oscillation tracks
the filter cutoff frequency. The cutoff frequency of
the filter can be accurately set according to the
resolution of the IC by measuring the frequency of
oscillation.
Features
Applications
Y Wide cutoff frequency range (0.8 MHz to
22.4 MHz)
Y Dual-channel architecture produces superior
matching and ease of use for quadrature signals
Y Companding design provides higher resolution at
lower cutoff frequencies
Y Low power consumption (<105 mA, typical 55 mA
from -5 V supply; Fc = 1 MHz @ 25°C)
Y Single ended or differential input operation
possible (AC coupled)
Y No external components for trimming necessary
Y Small package (16-pin SOP)
Y Digital Broadcasting Systems (DBS) and
Digital Video Broadcasting (DVB)
Y Satellite and cable TV decoders
Y Microwave point to point links
Block Diagram
4th Order
Butterworth
Filter
Fixed Gain
4th Order
Butterworth
Filter
Fixed Gain
Figure 1: Block Diagram
Rev. 2.1
November 1999
Free Datasheet http://www.Datasheet4U.com
1 page  
TH7301 Dual-Channel Programmable Low-Pass Filter
Definition of
Terms
Frequency
Setting
Gain Setting
fcset -
fc -
fstep -
Av -
cutoff frequency setting
cutoff frequency (-3dB bandwidth)
step size
voltage gain
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 kΩ between pin
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
fcset = 0.81875 MHz
The tables below show the selectable frequency
settings.
FC
(2..0)
000
001
010
011
1xx
Frequency range
fmin ... fmax (MHz)
0.8 ... 1.5937
1.6 ... 3.1875
3.2 ... 6.375
6.4 ... 12.75
12.8 ... 25.5
Step size
fstep (kHz)
6.25
12.5
25
50
100
FS
(6...0)
0000000
0000001
0000010
0000011
.
.
.
1111111
Step N
0
1
2
3
.
.
.
127
Cutoff Frequency
fcset = fmin + N*fstep
(MHz)
fcset = fmin
fcset = fmin + fstep
fcset = fmin + 2*fstep
fcset = fmin + 3*fstep
.
.
.
fcset = fmin + 127*fstep
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.
AC(2...0) Gain (dB)
000 18
001 15
010 12
011 9
100 6
101 3
110 0
111 -3
AC(5...3) Gain (dB)
000 2.5
001 2.0
010 1.5
011 1.0
100 0.5
101 0.0
110 0.0
111 0.0
5
Free Datasheet http://www.Datasheet4U.com
5 Page 
TH7301 Dual-Channel Programmable Low-Pass Filter
Filter
Characteristics
(continued)
Figure 9: initial gain accuracy (fcset = 0.8 MHz, fmeas = 0.2 MHz, VEE = -5.0 V, Ta = 23° C)
Figure 10: initial gain accuracy (fcset = 22.4 MHz, fmeas = 5.0 MHz, VEE = -5.0 V, Ta = 23° C)
11
Free Datasheet http://www.Datasheet4U.com
11 Page | ||
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| PDF Descargar | [ Datasheet TH7301.PDF ] | |
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