LTC1264-7CSW View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1264-7CSW' PDF : 16 Pages View PDF
LTC1264-7
APPLICATI S I FOR ATIO
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.
Table 8. Clock Feedthrough
VS
Single 5V
±5V
±7.5V
25:1
100µVRMS
100µVRMS
120µVRMS
50:1
100µVRMS
400µVRMS
1000µVRMS
Note: The clock feedthrough at 25:1 is imbedded in the wideband
noise of the filter. Clock waveform is a square wave.
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 passband and it
cannot be reduced with post filtering. For instance, the
LTC1264-7 wideband noise at ±5V supply is 160µVRMS,
145µVRMS 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
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.
12647fa
12
Share Link: 
