9

LTC1164-6

S

APPLICATI

I FOR ATIO

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 transient.

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 passband and it

cannot be reduced with post filtering. For instance, the

LTC1164-6 wideband noise at

90

the filter’s cutoff frequency. The total wideband noise

(

The clock feedthrough specifications are not part of the

wideband noise.

Speed Limitations

The LTC1164-6 optimizes AC performance versus power

consumption. To avoid op amp slew rate limiting at

maximum clock frequencies, the signal amplitude should

be kept below a specified level as shown on Table 4.

Aliasing

Aliasing is an inherent phenomenon of sampled data

systems and it occurs when input frequencies close to the

sampling frequency are applied. For the LTC1164-6 case,

±4%, will be aliased back into the filter’s passband. If, for

instance, an LTC1164-6 operating with a 100kHz clock

input signal, a 1.5kHz, 10

its output. When the LTC1164-6 operates with a clock-to-

cutoff frequency of 50:1, aliasing occurs at twice the clock

frequency. Table 5 shows details.

POWER SUPPLY

±7.5V

1.5MHz

1MHz

≥1MHz

±5V

1MHz

1MHz

Single 5V

1MHz

1MHz

INPUT FREQUENCY

OUTPUT LEVEL

OUTPUT FREQUENCY

(Relative to Input)

(Aliased Frequency)

(kHz)

(dB)

(kHz)

96

(or 104)

–75.0

4.0

97

(or 103)

– 68.0

3.0

98

(or 102)

– 65.0

2.0

98.5 (or 101.5)

– 60.0

1.5

99

(or 101)

– 3.2

1.0

99.5 (or 100.5)

– 0.5

0.5

192 (or 208)

– 76.0

8.0

194 (or 206)

– 68.0

6.0

196 (or 204)

– 63.0

4.0

198 (or 202)

– 3.4

2.0

199 (or 201)

– 1.3

1.0

199.5(or 200.5)

– 0.9

0.5

Table 6. Transient Response of LTC Lowpass Filters

DELAY

RISE

SETTLING OVER-

TIME*

TIME**

TIME***

SHOOT

LOWPASS FILTER

(SEC)

(SEC)

(SEC)

(%)

LTC1064-3 Bessel

0.5

LTC1164-5 Linear Phase

0

LTC1164-6 Linear Phase

1

LTC1264-7 Linear Phase

5

LTC1164-7 Linear Phase

5

LTC1064-7 Linear Phase

5

LTC1164-5 Butterworth

11

LTC1164-6 Elliptic

18

LTC1064-4 Elliptic

20

LTC1064-1 Elliptic

20

* To 50%

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