LTC1069-6

7

Rev. B

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APPLICATIONS INFORMATION

Temperature Behavior

The power supply current of the LTC1069-6 has a pos-

itive temperature coefficient. The GBW product of its

internal op amps is nearly constant and the speed of the

device does not degrade at high temperatures. Figure 4a,

Figure 4b and Figure 4c show the behavior of the pass-

band of the device for various supplies and temperatures.

The filter has a passband behavior which is temperature

independent.

Clock Feedthrough

The clock feedthrough is defined as the RMS value of

the clock frequency and its harmonics that are present

at the filter’s Output (Pin 8). The clock feedthrough is

tested with the Input (Pin 4) shorted to AGND (Pin 1) and

depends on PC board layout and on the value of the power

supplies. With proper layout techniques the values of the

clock feedthrough are shown in Table 2.

Table 2. Clock Feedthrough

VS

CLOCK FEEDTHROUGH

3.3V

100µVRMS

5V

170µVRMS

10V

350µVRMS

Any parasitic switching transients during the rising and

falling edges of the incoming clock are not part of the

clock feedthrough specifications. Switching transients

have frequency contents much higher than the applied

clock; their amplitude strongly depends on scope prob-

ing techniques as well as grounding and power supply

bypassing. The clock feedthrough can be reduced by

adding a single RC lowpass filter at the Output (Pin 8).

Wideband Noise

The wideband noise of the filter is the total RMS value of

the device’s noise spectral density and determines the

operating signal-to-noise ratio. The frequency contents

of the wideband noise lie within the filter’s passband.

The wideband noise cannot be reduced by adding post

filtering. The total wideband noise is nearly independent

of the clock frequency and depends slightly on the power

FREQUENCY (kHz)

1

1

2

17

1069-6 F04a

0

–1

–2

5

9

13

3

19

7

11

15

21

VS = SINGLE 3V

VIN = 0.5VRMS

fCLK = 500kHz

fCUTOFF = 10kHz

85°C

–40°C

(4a)

FREQUENCY (kHz)

1

1

2

17

1069-6 F04a

0

–1

–2

5

9

13

3

19

7

11

15

21

VS = SINGLE 5V

VIN = 1VRMS

fCLK = 750kHz

fCUTOFF = 15kHz

85°C

–40°C

FREQUENCY (kHz)

1

1

2

25

1069-6 F04c

0

–1

–2

7

13

19

4

28

10

16

22

31

VS = ±5V

VIN = 1.5VRMS

fCLK = 1MHz

fCUTOFF = 20kHz

85°C

–40°C

(4b)

(4c)

Figure 4.