LTC1066-1CS View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTC1066-1CS
Linear Technology
LTC1066-1CS Datasheet PDF : 16 Pages
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LTC1066-1
APPLICATIONS INFORMATION
and 18, and between pins 10 and 4, to isolate the
precision op amp supply pin from the switched-capaci-
tor network supply (see the Test Circuit).
0.2
0.1
0
VS = ±2.5V
VS = ±5V
–0.1
–0.2
–0.3
–0.4
VS = ±7.5V
–0.5
–0.6 LINEAR PHASE
–0.7
TA = 25°C
fCLK/fC = 100:1
–0.8
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
CLOCK FREQUENCY (MHz)
1066-1 F02
Figure 2. Output Offset Change vs Clock
(Relative to Offset for fCLK = 250kHz)
0.2
0
VS = ±2.5V
VS = ±5V
–0.2
–0.4
–0.6
VS = ±7.5V
–0.8
–1.0 TA = 25°C
fCLK/fC = 50:1
–1.2
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
CLOCK FREQUENCY (MHz)
1066-1 F03
Figure 3. Output Offset Change vs Clock
(Relative to Offset for fCLK = 250kHz)
AC PERFORMANCE
AC (Passband) Gain
The passband gain of the LTC1066-1 is equal to the
passband gain of the internal switched-capacitor lowpass
filter, and it is measured at f = 0.25fCUTOFF. Unlike conven-
tional monolithic filters, the LTC1066-1 starts with an
absolutely perfect 0dB DC gain and phases into an “imper-
fect” AC passband gain, typically ±0.1dB.
The filter’s low passband ripple, typically 0.05dB, is mea-
sured with respect to the AC passband gain.
The LTC1066-1 DC stabilizing loop slightly warps the
filter’s passband performance if the – 3dB frequency of the
feedback passive elements (1/2πRFCF) is more than the
cutoff frequency of the internal switched-capacitor filter
divided by 250. The LTC1066-1 clock tunability directly
relates to the above constraint. Figure 4 illustrates the
passband behavior of the LTC1066-1 and it demonstrates
the clock tunability of the device. A typical LTC1066-1
device was used to trace all four curves of Figure 4. Curve
D, for instance, has nearly zero ripple and 0.04dB pass-
band gain. Curve D’s 20kHz cutoff is much higher than the
8Hz cutoff frequency of the RFCF feedback network, so its
passband is free from any additional error due to RFCF
feedback elements. Curve B illustrates the passband error
when the 1MHz clock of curve D is lowered to 100kHz. A
0.1dB error is added to the filter’s original AC gain of
0.04dB.
1.00
TA = 25°C
0.75 fCLK/fC = 50:1
RF = 20k,
0.50 CF = 1µF
0.25
0
–0.25
AB C D
–0.50
–0.75
–1.00
10
100
1k
FREQUENCY (Hz)
10k 20k
CURVE
D:
fCUTOFF
=
20kHz
=
2500
×
1
2πRFCF
CURVE
C:
fCUTOFF
=
5kHz
=
625
×
1
2πRFCF
CURVE
B:
fCUTOFF
=
2kHz
=
250
×
1
2πRFCF
CURVE
A:
fCUTOFF
=
1kHz
=
125
×
1
2πRFCF
1066-1 F04
Figure 4. Passband Behavior
10
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