LTC1065 datasheet(11/20 Pages) AD

11 / 20 page

LTC1066-1

10661fa

APPLICATIONS INFORMATION

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 (1/2

πRFCF) is more than the

Figure 4. Passband Behavior

FREQUENCY (Hz)

100

10k 20k

1066-1 F04

1.00

0.75

0.50

0.25

–0.25

–0.50

–0.75

–1.00

TA = 25°C

fCLK/fC = 50:1

RF = 20k,

CF = 1µF

CURVE D: fCUTOFF = 20kHz = 2500 × 2πR

FCF

CURVE C: fCUTOFF = 5kHz = 625 × 2πR

FCF

CURVE B: fCUTOFF = 2kHz = 250 ×

πRFCF

CURVE A: fCUTOFF = 1kHz = 125 × 2πR

FCF

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 passband

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.

LTC1065 Datasheet(PDF) 11 Page - Analog Devices

LTC1065 Datasheet(HTML) 11 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL