LTC1064-4
Low Noise, 8th Order, Clock
Sweepable Cauer Lowpass Filter
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FEATURES
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DESCRIPTIO
8th Order Filter in a 14-Pin Package
80dB or More Stopband Attenuation at 2 × fCUTOFF
50:1, fCLK to fCUTOFF Ratio (Cauer)
100:1, fCLK to f–3dB Ratio (Transitional)
135µVRMS Total Wideband Noise
0.03% THD or Better
100kHz Maximum fCUTOFF Frequency
Operates up to ±8V Power Supplies
Input Frequency Range up to 50 Times the Filter
Cutoff Frequency
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APPLICATIO S
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Antialiasing Filters
Telecom Filters
Sinewave Generators
The LTC®1064-4 is an 8th order, clock sweepable Cauer
lowpass switched capacitor filter. An external TTL or
CMOS clock programs the value of the filter’s cutoff
frequency. With Pin 10 at V +, the fCLK to fCUTOFF ratio is
50:1; the filter has a Cauer response and with compensation the passband ripple is ±0.1dB. The stopband attenuation is 80dB at 2 × fCUTOFF. Cutoff frequencies up to
100kHz can be achieved. With Pin 10 at V –, the fCLK to
f –3dB ratio is 100:1, the filter has a transitional ButterworthCauer response with lower noise and lower delay
nonlinearity than the Cauer response. The stopband
attenuation at 2.5 × f –3dB is 92dB. Cutoff frequencies up to
50kHz can be achieved.
The LTC1064-4 features low noise and low harmonic
distortion even when input voltages up to 3VRMS are
applied. The LTC1064-4 overall performance competes
with equivalent multiple op amp active realizations. The
LTC1064-4 is pin compatible with the LTC1064-1,
LTC1064-2 and LTC1064-3.
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTCMOS is a trademark of Linear Technology Corporation.
The LTC1064-4 is manufactured using Linear Technology’s
enhanced LTCMOSTM silicon gate process.
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TYPICAL APPLICATIO
8th Order Clock Sweepable Lowpass Elliptic Filter
VIN
2
R(h, I)
INV C
VIN
COMP2*
14
13
0
3
8V
0.1µF
12
V–
AGND
4 + LTC1064-4
11
CLOCK
fCLK
V
(TTL, ≤5MHz)
5
10 + –
50/100
AGND
V /V
6
7
COMP1*
INV A
VOUT
NC
9
–8V
0.1µF
VOUT/VIN (dB)
1
Frequency Response
20
TA = 25°C
fCLK = 5MHz, 50:1
CCOMP1 = 30pF, CCOMP2 = 18pF
–20
–40
–60
fCLK = 2MHz, 50:1
VOUT
–80
8
–100
1064 TA01
* FOR FREQUENCIES ABOVE 20kHz AND MINIMUM PASSBAND RIPPLE REFER
TO THE PIN DESCRIPTION SECTION FOR COMPENSATION GUIDELINES.
NOTE:THE POWER SUPPLIES SHOULD BE BYPASSED BY A 0.1µF CAPACITOR
CLOSE TO THE PACKAGE. BYPASSING PIN 10 WITH 0.1µF CAPACITOR
REDUCES CLOCK FEEDTHROUGH. THE CONNECTION BETWEEN PINS 7
AND 14 SHOULD BE PHYSICALLY DONE UNDER THE PACKAGE.
fCLK = 1MHz, 100:1
1k
10k
100k
FREQUENCY (Hz)
1M
1064-4 TA01b
10644fb
1