LTC1069-1

7

10691fa

APPLICATIONS INFORMATION

Temperature Behavior

The power supply current of the LTC1069-1 has a positive

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. Figures 3a, 3b and

3c show the behavior of the maximum passband of the

device for various supplies and temperatures. The filter,

especially at ±5V supply, has a passband behavior which

is nearly 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 the AGND pin 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 on Table 2.

Table 2. Clock Feedthrough

CLOCK FEEDTHROUGH

3.3V

5V

±5V

160μVRMS

Any parasitic switching transients during the rise and

fall 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 probing tech-

niques as well as grounding and power supply bypassing.

The clock feedthrough can be reduced, if bothersome, by

adding a single RC lowpass filter at the output pin (8) of

the LTC1069-1.

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. Most of the wideband

noise frequency contents lie within the filter 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

supply voltage (see Table 3). The clock feedthrough speci

fications are not part of the wideband noise.

Table 3. Wideband Noise

WIDEBAND NOISE

3.3V

5V

±5V

Figure 3a

Figure 3b

Figure 3c

FREQUENCY (kHz)

0.5

6.5

10691 F03a

2.5

4.5

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

1.5

3.5

5.5

7.5

FREQUENCY (kHz)

0.5

6.5

10691 F03b

2.5

4.5

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

1.5

3.5

5.5

7.5 8.5 9.5 10.5

FREQUENCY (kHz)

1

13

10691 F03c

59

2.0

1.5

1.0

0.5

0

–0.5

–1.0

–1.5

–2.0

3

7

11

15