LTC1060CSW datasheet(18/20 Pages) LINER

18 / 20 page

LTC1060

1060fb

Figure 22. Combining Mode 3 with Mode 2b to Create a 4th

Order BR Elliptic Filter with 1dB Ripple and a Ratio of 0dB to

Stop Bandwidth Equal to 9/1.

Figure 23. Amplitude Response of the Notch Filter of Figure 22

Switched capacitor integrators generally exhibit higher

input offsets than discrete R, C integrators. These offsets

are mainly due to the charge injection of the CMOS

switches into the integrating capacitors and they are

temperature independent.

The internal op amp offsets also add to the overall offset

budget and they are typically a couple of millivolts. Be-

cause of this, the DC output offsets of switched capacitor

filters are usually higher than the offsets of discrete active

filters.

Figure 24 shows half of an LTC1060 filter building block

with its equivalent input offsets VOS1, VOS2, VOS3. All three

are 100% tested for both sides of the LTC1060. VOS2 is

generally the larger offset. When the SA/B, Pin 6, of the

LTC1060 is shorted to the negative supply (i.e., mode 3),

the value of the VOS2 decreases. Additionally, with SA/B

low, a 20% to 30% noise reduction is observed. Mode 1

can still be achieved, if desired, by shorting the S1 pin to

the lowpass output (Figure 25).

LTC1060 • CM04

VIN

R31

R21

R52

R32

V+ = – 5V

–5V

VOUT

T2L OR CMOS

CLOCK IN

R41

RL1

RH1

R22

R62

R42

LPA

BPA

HPA

INVA

S1A

SA/B

LSh

CLKA

LPB

BPB

INVB

S1B

AGND

–

50/100

CLKB

LTC1060

R11

RESISTOR VALUES

R11 = 60k

R41 = 28.84k

R52 = 5k

R32 = 455.75k

R21 = 5k

RH1 = 5k

R62 = 1.59k

R42 = 503.85k

R31 = 54.75k

RL1 = 19.3k

R22 = 60k

V– = – 5V

0.7

–30

–20

–10

1.1

1.2

1.3

–60

–50

–40

0.9

0.8

f0 = 1.0

INPUT FREQUENCY NORMALIZED TO FILTER CENTER FREQUENCY

TLC1060 • CMO05

fCLK

200

=; fCLK ≤ 1MHz

(17)

–

(18)

(16)

(19)

(20)

VOS1

VOS2

TLC1060 • LO01

–

VOS3

Figure 24. Equivalent Input Offsets of 1/2 LTC1060 Filter

Building Block

Figure 25. Mode 1(LN): Same Operation as Mode 1 but Lower

VOS2 Offset and Lower Noise

LTC1060 OFFSETS

COMM E TS ON THE M ODES OF OPERATIO

1/2 LTC1060

SA/B

VIN

–

(18)

(20)

(19)

S1A

(16)

V –

(17)

TLC1060 • LO02

∫

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