LTC1061AC Просмотр технического описания (PDF) - Linear Technology
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LTC1061AC Datasheet PDF : 16 Pages
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LTC1061
W
U
ODES OF OPERATIO
1
R33 2
R23 3
Rl2
Rh2
20
R42
19
R32
18
R22
4
17
T2L, CMOS
CLOCK INPUT
5
16
LTC1061
6
15
V–
Rl1
7
14
R41
8
13
R31
9
12
R21
V+
10
11
Rh1
VIN
NOTES: FOR NOTCH RESPONSES, PIN 7 SHOULD BE
PREFERABLY CONNECTED TO GROUND AND THE
FILTER OUTPUT IS PIN 3.
FOR BANDPASS OR LOWPASS RESPONSES, PIN 7
CAN BE EITHER AT GROUND OR POSITIVE SUPPLY,
AND THE FILTER OUTPUT IS PIN 2 OR PIN 1.
R11
1061 F12
Figure 12. 6th Order Elliptic Bandpass, Lowpass
or Notch Topology
Figure 13 shows the measured frequency response of the
circuit Figure 12 configured to provide a notch function.
The filter output is taken out of pin 3. The resistor values
are standard 1%.
The ratio of the 0dB width, BW1, to the notch width BW2,
is 5:1 and matches the theoretical design value. The
measured notch depth was –53dB versus –56dB theoreti-
cal and the clock-to-center notch frequency ratio is 100:1.
Figure 14 shows the measured frequency response of the
circuit topology, Figure 12, but with pole/zero locations
configured to provide a high Q, 6th order elliptic bandpass
filter operating with a clock-to-center frequency ratio of
50:1 or 100:1. The theoretical passband ripple, stopband
attenuation and stopband to ripple bandwidth ratio are
0.5dB, 56dB, 5:1 respectively. The obtained results with
1% standard resistor values closely match the theoretical
frequency response. For this application, the normalized
center frequencies, Qs, and notch frequencies are (fO1 =
0.969, Q1 = 54.3, fn1 = 0.84, fO2 = 1.031, Q2 = 54.3, fn2 =
1.187, fO3 = 1, Q3 = 26.2). The output of the filter is the BP
output of Side A, Pin 2.
Lowpass filters with stopband notches can also be realized
by using Figure 12 provided that 6th order lowpass filter
approximations with 2 stopband notches can be synthe-
sized. Literature describing elliptic double terminated (RLC)
0
BW1
–10
–20
–30
–40
–50
BW2
–60 VS = ±5V
fCLK = 260kHz
–70
1.0 1.5 2.0
2.6kHz
2.5 3.0
fIN (kHz)
STANDARD 1%
RESISTOR VALUES
R11 = 165k
R31 = 143k
Rh1 = 10k
R22 = 20k
R42 = 15.4k
Rl2 = 10k
R33 = 169k
R21 = 10k
R41 = 13k
Rl1 = 10.5k
R32 = 221k
Rh2 = 10.5k
R23 = 84.5k
NOTES: USE A 15pF CAPACITOR
BETWEEN PINS 17 AND 18.
PIN 7 IS GROUNDED.
3.5
1061 F13
Figure 13. Resistor Values and Amplitude Response of
Figure 12 Topology. The Notch is Centered at 2600Hz.
0
VS = ±5V
fCLK = 130kHz
–10
–20
–30
–40
–50
–60
–70
STANDARD 1%
RESISTOR VALUES
R11 = 576k
R31 = 562k
Rh11 = 28.7k
R22 = 10.7k
R42 = 10k
Rl2 = 10k
R33 = 75k
R21 = 10k
R41 = 10.7k
Rl11 = 40.2k
R32 = 562k
Rh2 = 14k
R23 = 2.94k
NOTE: FOR CLOCK FREQUENCIES
ABOVE 500kHz, CONNECT A 5pF
IN PARALLEL WITH R41 AND R42.
–80
–90
1.0 1.5 2.0 2.5 3.0 3.5
fIN (kHz)
1061 F14
Figure 14. Resistor Values and Amplitude Response of Figure 12
Topology. The Bandpass Filter is Centered Around 2600Hz when
Operating with a 130kHz Clock.
1061fe
10
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