LTC1264-7
Linear Phase, Group Delay
Equalized, 8th Order
Lowpass Filter
FEATURES
■
■
■
■
■
■
■
■
DESCRIPTIO
Steeper Roll-Off Than Bessel Filters
High Speed: f
C
≤
200kHz
Phase Equalized Filter in a 14-Pin Package
Phase and Group Delay Response Fully Tested
Transient Response Exhibits 5% Overshoot and
No Ringing
65dB THD or Better Throughout a 100kHz Passband
No External Components Needed
Available in Plastic 14-Pin DIP and 16-Pin SO
Wide Packages
The LTC1264-7 is a clock-tunable monolithic 8th order
lowpass filter with linear passband phase and flat group
delay. The amplitude response approximates a maximally
flat passband and exhibits steeper roll-off than an equiva-
lent 8th order Bessel filter. For instance, at twice the cutoff
frequency, the filter attains 28dB attenuation (vs 12dB for
Bessel), while at three times the cutoff frequency, the filter
attains 55dB attenuation (vs 30dB for Bessel).
The cutoff frequency of the LTC1264-7 is tuned via an
external TTL or CMOS clock. The clock-to-cutoff
frequency ratio of the LTC1264-7 can be set to 25:1 (pin
10 to V
+
) or 50:1 (pin 10 to V
–
). When the filter operates
at clock-to-cutoff frequency ratio of 25:1, the input is
double-sampled to lower the risk of aliasing.
The LTC1264-7 is optimized for speed. Depending on the
operating conditions, cutoff frequencies between 200kHz
and 250kHz can be obtained. (Please refer to the Passband
vs Clock Frequency graphs.)
The LTC1264-7 is pin-compatible with the LTC1064-X
series.
APPLICATIO S
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Data Communication Filters
Time Delay Networks
Phase Matched Filters
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
1
V
IN
2
3
8V
4
5
6
7
LTC1264-7
14
13
12
11
10
9
8
4-Level PAM Eye Diagram
200kHz Linear Phase Lowpass Filter
–8V
8V
V
OUT
1264-7 TA01
NOTE: THE POWER SUPPLIES SHOULD BE BYPASSED BY A
0.1µF CAPACITOR CLOSE TO THE PACKAGE AND ANY PRINTED
CIRCUIT BOARD ASSEMBLY SHOULD MAINTAIN A DISTANCE
OF AT LEAST 0.2 INCHES BETWEEN ANY OUTPUT OR INPUT
PIN AND THE f
CLK
LINE.
1V/DIV
f
CLK
= 5MHz
f
CLK
= 5MHz
f
C
= 200kHz
12647fa
U
500ns/DIV
1264-7 TA02
U
U
1
LTC1264-7
ABSOLUTE
AXI U
RATI GS
(Note 1)
Operating Temperature Range
LTC1264-7C ...................................... – 40°C to 85°C
LTC1264-7M
(OBSOLETE)
.............. – 55°C to 125°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Total Supply Voltage (V
+
to V
–
) .......................... 16.5V
Power Dissipation ............................................. 400mW
Burn-In Voltage ................................................... 16.5V
Voltage at Any Input ..... (V
–
– 0.3V)
≤
V
IN
≤
(V
+
+ 0.3V)
Storage Temperature Range ............... – 65°C to 150°C
PACKAGE/ORDER I FOR ATIO
TOP VIEW
NC
V
IN
GND
V
+
NC
LP (A)
R
IN
(A)
1
2
3
4
5
6
7
14 OUT (C)
13 NC
12 V
–
11 f
CLK
10 25/50
9
8
V
OUT
NC
ORDER PART
NUMBER
LTC1264-7CN
NC 1
V
IN
2
GND 3
V
+
4
NC 5
NC 6
LP (A) 7
R
IN
(A) 8
N PACKAGE
14-LEAD PLASTIC DIP
T
JMAX
= 110°C,
θ
JA
= 65°C/W (N )
J PACKAGE
14-LEAD CERAMIC DIP
T
JMAX
= 150°C,
θ
JA
= 65°C/W (J )
LTC1264-7CJ
LTC1264-7MJ
OBSOLETE PACKAGE
Consider the N14 Package for Alternate Source
Order Options
Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Passband Gain
Gain at 0.50 f
CUTOFF
(Note 4)
Gain at 0.75 f
CUTOFF
Gain at f
CUTOFF
Gain at 2.0 f
CUTOFF
Gain with f
CLK
= 20kHz
Gain with f
CLK
= 400kHz, V
S
=
±2.375V
Gain with f
CLK
= 4MHz
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. V
S
=
±7.5V,
R
L
= 10k, f
CUTOFF
= 100kHz or 50kHz, f
CLK
= 2.5MHz, TTL or
CMOS level (maximum clock rise or fall time
≤
1µs) and all gain measurements are referenced to passband gain, unless otherwise
specified.
CONDITIONS
0.1Hz
≤
f
≤
0.25 f
CUTOFF
f
TEST
= 25kHz, (f
CLK
/ f
C
) = 25:1
f
TEST
= 50kHz, (f
CLK
/ f
C
) = 25:1
f
TEST
= 25kHz, (f
CLK
/ f
C
) = 50:1
f
TEST
= 75kHz, (f
CLK
/ f
C
) = 25:1
f
TEST
= 100kHz, (f
CLK
/ f
C
) = 25:1
f
TEST
= 50kHz, (f
CLK
/ f
C
) = 50:1
f
TEST
= 200kHz, (f
CLK
/ f
C
) = 25:1
f
TEST
= 100kHz, (f
CLK
/ f
C
) = 50:1
f
TEST
= 200Hz, (f
CLK
/ f
C
) = 50:1
f
TEST
= 8kHz, (f
CLK
/ f
C
) = 25:1
f
TEST
= 16kHz, (f
CLK
/ f
C
) = 25:1
f
TEST
= 160kHz, V
IN
= 1V
RMS
(f
CLK
/ f
C
) = 25:1, T
A
= 0°C to 70°C
(f
CLK
/ f
C
) = 25:1
MIN
●
●
●
●
●
●
●
●
2
U
U
W
W W
U
W
TOP VIEW
16 OUT (C)
15 NC
14 V
–
13 NC
12 f
CLK
11 25/50
10 NC
9
V
OUT
ORDER PART
NUMBER
LTC1264-7CSW
SW PACKAGE
16-LEAD PLASTIC SO WIDE
T
JMAX
= 110°C,
θ
JA
= 85°C/W
TYP
– 0.10
– 0.15
–1.0
– 3.0
– 3.0
– 28
– 30
– 0.3
0.15
– 2.70
0.00
±1.0
MAX
0.50
0.20
0.30
0.1
–1.9
– 2.3
– 20
– 27
0.1
0.5
– 1.4
UNITS
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
12647fa
– 0.50
– 0.50
– 0.65
– 1.5
– 3.7
– 4.5
– 34
– 34
– 0.7
– 0.2
– 3.5
●
3.0
LTC1264-7
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
S
=
±7.5V,
R
L
= 10k, f
CUTOFF
= 100kHz or 50kHz, f
CLK
= 2.5MHz, TTL or
CMOS level (maximum clock rise or fall time
≤
1µs) and all gain measurements are referenced to passband gain, unless otherwise
specified.
PARAMETER
Phase Factor (F )
Phase = 180° –
F
(f/f
C
)
(Note 2)
Phase Nonlinearity
(Note 2)
CONDITIONS
(f
CLK
/ f
C
) = 25:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 50:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 25:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 50:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 25:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 50:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 25:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 50:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 25:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 50:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 25:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 50:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 25:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 50:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 25:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 50:1, f
≤
f
CUTOFF
(f
CLK
/ f
C
) = 25:1
(f
CLK
/ f
C
) = 50:1
V
S
= Single 5V (GND = 2V)
V
S
=
±5V
V
S
=
±
7.5V
25:1,
±7.5V,
f = f
CLK
V
S
= Single 5V
V
S
=
±5V
V
S
=
±
7.5V
V
S
=
±2.375V
V
S
=
±5V
V
S
=
±7.5V
25:1, V
S
=
±5V
50:1, V
S
=
±5V
25:1, V
S
=
±5V
50:1, V
S
=
±5V
V
S
=
±2.375V
V
S
=
±5V
V
S
=
±7.5V
Power Supply Range
MIN
TYP
407
±
2
388
±
2
±1.0
±1.0
●
●
ELECTRICAL CHARACTERISTICS
MAX
●
●
392
374
423
414
±
2.0
±
2.0
Group Delay (t
d
)
t
d
= (F / 360)(1/f
C
);
(Note 3, 4)
Group Delay Ripple
(Note 3)
11.3
21.6
●
●
10.9
20.8
±1.0
±1.0
11.7
22.9
●
●
±
2.0
±
2.0
Input Frequency Range
(Table 9, 10)
Maximum f
CLK
Clock Feedthrough
Wideband Noise
(1Hz
≤
f < f
CLK
)
Input Impedance
Output DC Voltage Swing
(Note 5)
Output DC Offset
(f
CLK
= 1MHz)
Output DC Offset TempCo
Power Supply Current
(f
CLK
= 1MHz)
45
●
●
±2.0
±3.0
<f
CLK
<f
CLK
/2
2
3
5
120
140
±
5%
160
±
5%
175
±
5%
65
±1.0
±2.3
±3.8
±100
±100
±200
±200
11
14
87
±220
±220
●
●
17
●
±2.375
22
22
23
26
28
32
±8
UNITS
Deg
Deg
Deg
Deg
%
%
%
%
µs
µs
µs
µs
%
%
%
%
kHz
kHz
MHz
MHz
MHz
µV
RMS
µV
RMS
µV
RMS
µV
RMS
kΩ
V
V
V
mV
mV
µV/°C
µV/°C
mA
mA
mA
mA
mA
mA
V
12647fa
3
LTC1264-7
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Input frequencies, f, are linearly phase shifted through the filter as
long as f
≤
f
C
; f
C
= cutoff frequency.
Figure 1 curve (A) shows the typical phase response of an LTC1264-7
operating at f
CLK
= 2.5MHz, f
C
= 100kHz. An endpoint straight line, curve
(B), depicts the ideal linear phase response of the filter. It is described by:
phase shift = 180° –
F
(f/f
C
); f
≤
f
C
.
F
is arbitrarily called the “phase factor” expressed in degrees. The phase
factor together with the specified deviation from the ideal straight line
allows the calculation of the phase at a given frequency. Note, the
maximum phase nonlinearity, Figure 1, occurs at the vicinity of f = 0.25 f
C
and = 0.75 f
C
. Example: The phase shift at 70kHz of the LTC1264-7 shown
in Figure 1 is: phase shift = 180° – 407° (70kHz/100kHz)
±
nonlinearity =
–104.9°
±
1% or –104.9°
±
1.05°.
Note 3:
Group delay and group delay deviation are calculated from the
measured phase factor and phase deviation specifications.
Note 4:
The filter cutoff frequency is abbreviated as f
CUTOFF
or f
C
.
Note 5:
The AC swing is typically 9V
P-P
, 5.6V
P-P
, 1.8V
P-P
with
±
7.5V,
±
5V,
±
2.5V supply respectively. For more information refer to the THD + Noise
vs Input graphs.
180
90
0
–90
A
B
f
CLK
= 2.5MHz
(f
CLK
/f
C
) = 25:1
PHASE (DEG)
–180
–270
–360
0 10 20
30 40 50 60 70 80 90 100
FREQUENCY (kHz)
LTC1264-7 F01
Figure 1. Phase Response in the Passband (Note 2)
12647fa
4
LTC1264-7
TYPICAL PERFOR A CE CHARACTERISTICS
Gain vs Frequency
10
0
–10
–20
PHASE FACTOR
V
S
=
±7.5V
f
CLK
= 1MHz
T
A
= 25°C
GAIN (dB)
–30
–40
–50
–60
–70
–80
–90
–100
1
10
100
FREQUENCY (kHz)
1000
1264-7 G01
PHASE FACTOR
50:1
25:1
Phase Factor vs f
CLK
(Min and
Max Representative Units)
450
445
440
435
V
S
=
±7.5V
(f
CLK
/f
C
) = 25:1
T
A
= 25°C
PHASE FACTOR
430
425
420
415
410
405
400
395
0
1
3
2
f
CLK
(MHz)
4
5
1264-7 G04
PHASE FACTOR
Passband Gain and Phase
3
2
1
0
GAIN (dB)
–1
–2
–3
–4
–5
–6
V
S
=
±7.5V
f
CLK
= 2.5MHz
f
C
= 100kHz
(f
CLK
/f
C
) = 25:1
PHASE
GAIN
180
135
90
45
PHASE (DEG)
GAIN (dB)
0
–45
–90
–135
–180
–225
3
2
1
0
–1
–2
–3
–4
–5
–6
–7
–270
–7
10 20 30 40 50 60 70
80
90 100 110
FREQUENCY (kHz)
1264-7 G06
U W
Phase Factor vs f
CLK
(Typical Unit)
460
450
440
430
420
410
400
390
0
1
3
2
f
CLK
(MHz)
4
5
1264-7 G02
Phase Factor vs f
CLK
(Typical Unit)
450
440
70°C
430
25°C
420
410
0°C
400
390
380
370
0
1
3
2
f
CLK
(MHz)
4
5
1264-7 G03
V
S
=
±7.5V
(f
CLK
/f
C
) = 25:1
V
S
=
±7.5V
(f
CLK
/f
C
) = 50:1
70°C
25°C
0°C
Phase Factor vs f
CLK
(Min and
Max Representative Units)
425
420
415
410
405
400
395
V
S
=
±5V
(f
CLK
/f
C
) = 25:1
T
A
= 25°C
0
0.5
1.0
1.5
2.0
f
CLK
(MHz)
2.5
3.0
1264-7 G05
Passband Gain and Phase
180
135
90
45
GAIN
PHASE (DEG)
0
–45
PHASE
V
S
=
±7.5V
f
CLK
= 2.5MHz
f
C
= 50kHz
(f
CLK
/f
C
) = 50:1
5
–90
–135
–180
–225
–270
10 15 20 25 30 35 40 45 50 55
FREQUENCY (kHz)
1264-7 G07
12647fa
5
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