LTC1264-7
Linear Phase, Group Delay
Equalized, 8th Order
Lowpass Filter
FEATURES
s
s
s
s
s
DESCRIPTIO
s
s
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
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.
APPLICATI
s
s
s
S
Data Communication Filters
Time Delay Networks
Phase Matched Filters
TYPICAL APPLICATI
1
V
IN
2
3
8V
4
5
6
7
LTC1264-7
4-Level PAM Eye Diagram
14
13
12
11
10
9
8
1264-7 TA01
200kHz Linear Phase Lowpass Filter
–8V
f
CLK
= 5MHz
8V
V
OUT
1V/DIV
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.
f
CLK
= 5MHz
f
C
= 200kHz
U
500ns/DIV
1264-7 TA02
UO
UO
1
LTC1264-7
ABSOLUTE
AXI U
RATI GS
(Note 1)
Operating Temperature Range
LTC1264-7C ...................................... – 40°C to 85°C
LTC1264-7M ................................... – 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
LTC1264-7CJ
LTC1264-7MJ
J PACKAGE
14-LEAD CERAMIC DIP
N PACKAGE
14-LEAD PLASTIC DIP
T
JMAX
= 150°C,
θ
JA
= 65°C/W (J )
T
JMAX
= 110°C,
θ
JA
= 65°C/W (N )
ELECTRICAL CHARACTERISTICS
PARAMETER
Passband Gain
Gain at 0.50 f
CUTOFF
(Note 3)
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
V
S
=
±7.5V,
R
L
= 10k, T
A
= 25°C, 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
(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
MIN
q
q
q
q
q
q
q
q
Phase Factor (F )
Phase = 180° –
F
(f/f
C
)
(Note 1)
Phase Nonlinearity
(Note 1)
2
U
U
W
W W
U
W
TOP VIEW
NC 1
V
IN
2
GND 3
V
+
4
NC 5
NC 6
LP (A) 7
R
IN
(A) 8
16 OUT (C)
15 NC
14 V
–
13 NC
12 f
CLK
11 25/50
10 NC
9
S PACKAGE
16-LEAD PLASTIC SOL
V
OUT
ORDER PART
NUMBER
LTC1264-7CS
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
Deg
Deg
Deg
Deg
%
%
%
%
– 0.50
– 0.50
– 0.65
– 1.5
– 3.7
– 4.5
– 34
– 34
– 0.7
– 0.2
– 3.5
q
3.0
407
±
2
388
±
2
q
q
392
374
±1.0
±1.0
423
414
q
q
±
2.0
±
2.0
LTC1264-7
ELECTRICAL CHARACTERISTICS
V
S
=
±7.5V,
R
L
= 10k, T
A
= 25°C, 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
Group Delay (t
d
)
t
d
= (F / 360)(1/f
C
);
(Note 2, 3)
Group Delay Ripple
(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
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
q
MIN
TYP
11.3
21.6
MAX
q
q
10.9
20.8
±1.0
±1.0
11.7
22.9
q
q
±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 4)
Output DC Offset
(f
CLK
= 1MHz)
Output DC Offset TempCo
Power Supply Current
(f
CLK
= 1MHz)
30
q
q
±2.0
±3.0
<f
CLK
<f
CLK
/2
2
3
5
120
140
±
5%
160
±
5%
175
±
5%
50
±1.0
±2.3
±3.8
±100
±100
±200
±200
11
14
17
75
±220
±220
q
V
S
=
±7.5V
q
Power Supply Range
The
q
denotes specifications which apply over the full operating temperature range.
Note 1:
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 2:
Group delay and group delay deviation are calculated from the measured phase
factor and phase deviation specifications.
Note 3:
The filter cutoff frequency is abbreviated as f
CUTOFF
or f
C
.
Note 4:
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.
±2.375
22
22
23
26
28
32
±8
UNITS
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
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 1)
3
LTC1264-7
TYPICAL PERFOR A CE CHARACTERISTICS
Gain vs Frequency
10
0
–10
–20
PHASE FACTOR
GAIN (dB)
V
S
= ±7.5V
f
CLK
= 1MHz
T
A
= 25°C
–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
PHASE FACTOR
430
425
420
415
410
405
400
395
0
1
3
2
f
CLK
(MHz)
4
5
1264-7 G04
V
S
= ±7.5V
(f
CLK
/f
C
) = 25:1
T
A
= 25°C
PHASE FACTOR
Passband Gain and Phase
3
2
1
0
GAIN (dB)
–2
–3
–4
–5
–6
V
S
= ±7.5V
f
CLK
= 2.5MHz
f
C
= 100kHz
(f
CLK
/f
C
) = 25:1
PHASE
–45
–90
–135
–180
–225
GAIN (dB)
–1
–270
–7
10 20 30 40 50 60 70 80 90 100 110
FREQUENCY (kHz)
1264-7 G06
4
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
3
2
1
0
–1
–2
–3
–4
–5
–6
–7
5
V
S
= ±7.5V
f
CLK
= 2.5MHz
f
C
= 50kHz
(f
CLK
/f
C
) = 50:1
PHASE
GAIN
PHASE (DEG)
180
135
90
45
PHASE (DEG)
GAIN
0
0
–45
–90
–135
–180
–225
–270
10 15 20 25 30 35 40 45 50 55
FREQUENCY (kHz)
1264-7 G07
LTC1264-7
TYPICAL PERFOR A CE CHARACTERISTICS
Passband Gain vs f
CLK
5
4
3
2
V
S
= ±7.5V
(f
CLK
/f
C
) = 25:1
T
A
= 25°C
A. f
CLK
= 1MHz
B. f
CLK
= 2MHz
C. f
CLK
= 3MHz
D. f
CLK
= 4MHz
E. f
CLK
= 5MHz
5
4
3
2
V
S
= ±7.5V
(f
CLK
/f
C
) = 50:1
T
A
= 25°C
A. f
CLK
= 1MHz
B. f
CLK
= 2MHz
C. f
CLK
= 3MHz
D. f
CLK
= 4MHz
E. f
CLK
= 5MHz
GAIN (dB)
GAIN (dB)
0
–1
–2
–3
–4
–5
10
100
FREQUENCY (kHz)
1000
1264-7 G08
0
–1
–2
A
B
C D E
GAIN (dB)
1
A
B
C
D E
Passband Gain vs f
CLK
at 85°C
5
4
3
2
V
S
= ±5V
(f
CLK
/f
C
) = 25:1
A. f
CLK
= 1MHz
B. f
CLK
= 2MHz
C. f
CLK
= 3MHz
10
0
–10
–20
GAIN (dB)
GAIN (dB)
0
–1
–2
A
–3
–4
–5
10
100
FREQUENCY (kHz)
1000
1264-7 G11
–40
–50
–60
V
S
= ±7.5V
f
CLK
= 5MHz
(f
CLK
/f
C
) = 25:1
T
A
= 25°C
10
100
FREQUENCY (kHz)
1000
1264-7 G12
GAIN (dB)
1
B
C
Gain vs f
CLK
10
0
–10
–20
GAIN (dB)
A
B
GAIN (dB)
GAIN (dB)
–30
–40
–50
–60
–70
–80
–90
10
FREQUENCY (kHz)
1264-7 G14
A. f
CLK
= 0.5MHz
B. f
CLK
= 1MHz
C. f
CLK
= 2MHz
V
S
= SINGLE 5V
(f
CLK
/f
C
) = 25:1
AGND = 2V
T
A
= 25°C
100
200
U W
C
Passband Gain vs f
CLK
5
4
3
2
1
0
–1
–2
–3
–4
–5
10
100
FREQUENCY (kHz)
1000
1264-7 G09
Passband Gain vs f
CLK
at 85°C
V
S
= ±7.5V
(f
CLK
/f
C
) = 25:1
A. f
CLK
= 4MHz
B. f
CLK
= 5MHz
1
A
B
–3
–4
–5
10
100
FREQUENCY (kHz)
1000
1264-7 G10
Gain vs Frequency
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
Gain vs Frequency
–30
–70
–80
–90
V
S
= ±5V
f
CLK
= 3MHz
(f
CLK
/f
C
) = 25:1
T
A
= 25°C
10
100
FREQUENCY (kHz)
1000
1264-7 G13
Passband Gain vs f
CLK
5
4
3
2
1
0
–1
–2
–3
–4
–5
10
FREQUENCY (kHz)
1264-7 G15
Maximum Passband vs
Temperature
2
1
A
0
–1
–2
–3
A. T
A
= 70°C
B. T
A
= –40°C
V
S
= SINGLE 5V
f
CLK
= 2MHz
(f
CLK
/f
C
) = 25:1
AGND = 2V
1
10
FREQUENCY (kHz)
100
1264-7 G16
V
S
= SINGLE 5V
(f
CLK
/f
C
) = 25:1
AGND = 2V
T
A
= 25°C
A. f
CLK
= 0.5MHz
B. f
CLK
= 1.0MHz
C. f
CLK
= 1.5MHz
D. f
CLK
= 2.0MHz
B
A
B
C
D
–4
–5
100
200
5
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