11

LTC1164-7

11647fb

S

APPLICATI

I FOR ATIO

Table 8. Clock Feedthrough

VS

50:1

100:1

Single 5V

70

µVRMS

70

µVRMS

±5V

100

µVRMS

200

µVRMS

±7.5V

120

µVRMS

500

µVRMS

Note: The clock feedthrough at Single 5V is imbedded in the wideband

noise of the filter. The clock waveform is a square wave.

Clock Feedthrough

Clock feedthrough is defined as the RMS value of the clock

frequency and its harmonics that are present at the filter’s

output pin (9). The clock feedthrough is tested with the

input pin (2) grounded and it 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 8.

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 fre-

quency contents much higher than the applied clock; their

amplitude strongly depends on scope probing techniques

as well as grounding and power supply bypassing. The

clock feedthrough, if bothersome, can be greatly reduced

by adding a simple R/C lowpass network at the output of

the filter pin (9). This R/C will completely eliminate any

switching transients.

Wideband Noise

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

the device’s noise spectral density and it is used to

determine the operating signal-to-noise ratio. Most of its

frequency contents lie within the filter’s passband and

cannot be reduced with post filtering. For instance, the

LTC1164-7 wideband noise at

±5V supply is 105µVRMS,

95

µVRMS of which have frequency contents from DC up to

the filter’s cutoff frequency. The total wideband noise

(

µVRMS) is nearly independent of the value of the clock.

The clock feedthrough specifications are not part of the

wideband noise.

Speed Limitations

The LT1164-7 optimizes AC performance vs power con-

sumption. To avoid op amp slew rate limiting at maximum

clock frequencies, the signal amplitude should be kept

below a specified level as shown in Table 9.

Table 9. Maximum VIN vs VS and Clock

POWER SUPPLY

MAXIMUM fCLK

MAXIMUM VIN

±7.5V

1MHz

2.0VRMS (fIN > 20kHz)

0.7VRMS (fIN > 250kHz)

±5V

1MHz

1.4VRMS (fIN > 20kHz)

0.5VRMS (fIN > 100kHz)

Single 5V

1MHz

0.5VRMS (fIN > 100kHz)

Table 10. Transient Response of LTC Lowpass Filters

DELAY

RISE

SETTLING OVER-

TIME*

TIME**

TIME***

SHOOT

LOWPASS FILTER

(SEC)

(SEC)

(SEC)

(%)

LTC1064-3 Bessel

0.50/fC

0.34/fC

0.80/fC

0.5

LTC1164-5 Bessel

0.43/fC

0.34/fC

0.85/fC

0

LTC1164-6 Bessel

0.43/fC

0.34/fC

1.15/fC

1

LTC1264-7 Linear Phase

1.15/fC

0.36/fC

2.05/fC

5

LTC1164-7 Linear Phase

1.20/fC

0.39/fC

2.20/fC

5

LTC1064-7 Linear Phase

1.20/fC

0.39/fC

2.20/fC

5

LTC1164-5 Butterworth

0.80/fC

0.48/fC

2.40/fC

11

LTC1164-6 Elliptic

0.85/fC

0.54/fC

4.30/fC

18

LTC1064-4 Elliptic

0.90/fC

0.54/fC

4.50/fC

20

LTC1064-1 Elliptic

0.85/fC

0.54/fC

6.50/fC

20

* To 50%

±5%, ** 10% to 90% ±5%, *** To 1% ±0.5%