LTC1065 Linear Technology, LTC1065 Datasheet - Page 10

• Manufacturer Part Number: LTC1065
• Description: DC Accurate/ Clock-Tunable Linear Phase 5th Order Bessel Lowpass Filter
• Manufacturer: Linear Technology

The above data is valid for clock frequencies up to 800kHz, 900kHz, 1MHz, for
V
Clock Feedthrough
Clock feedthrough is defined as the RMS value of the clock
frequency and its harmonics which are present at the
filter’s output pin. The clock feedthrough is tested with the
filter input grounded and it depends on the quality of the
PC board layout and power supply decoupling. Any para-
sitic switching transients during the rise and fall of the
incoming clock, are not part of the clock feedthrough
specifications; their amplitude strongly depends on scope
probing techniques as well as ground quality and power
supply bypassing. For a power supply V
feedthrough of the LTC1065 is 50 V
the clock feedthrough approaches 75 V
and 9 show a typical scope photo of the LTC1065 output
pin when the input pin is grounded. The filter cutoff
frequency was 1kHz, while scope bandwidth was chosen
to be 1MHz so that switching transients above the 100kHz
clock frequency would show.
Wideband Noise
The wideband noise data is used to determine the operat-
ing signal-to-noise ratio at a given distortion level. The
wideband noise ( V
of the clock frequency and excludes the clock feedthrough.
The LTC1065’s typical wideband noise is 80 V
9 shows the same scope photo as Figure 8 but with a more
sensitive vertical scale. The clock feedthrough is imbed-
ded in the filter’s wideband noise. The peak-to-peak wide-
band noise of the filter can be clearly seen; it is approxi-
mately 420 V
wideband noise of the part multiplied by a crest factor
of 5.25.
LTC1065
Table 3. CMR Data, f
POWER SUPPLY
10
A
S
= 2.5V, 5V, 7.5V respectively.
PPLICATI
2.5V
5V
7.5V
P-P
1.8V
. Note that 420 V
O
V
4V
6V
IN
CLK
RMS
U
= 100kHz
S
– 40 C
84dB
82dB
80dB
) is nearly independent of the value
I FOR ATIO
U
83dB
78dB
77dB
25 C
P-P
RMS
W
equals the 80 V
85 C
80dB
77dB
76dB
S
; for V
= 5V, the clock
RMS
. Figures 8
RMS
(V
S
OS
= 7.5V,
U
83dB
78dB
80dB
25 C
. Figure
Nulled)
RMS
Aliasing
Aliasing is an inherent phenomenon of sampled data
filters. It primarily occurs when the frequency of an input
signal approaches the sampling frequency. For the
LTC1065, an input signal whose frequency is in the range
of f
passband and stopband. Table 4 shows details.
Example:
CLK
Figure 9. LTC1065 Output Clock Feedthrough + Noise
Figure 8. LTC1065 Output Clock Feedthrough + Noise
f
CLK
6% will generate an alias signal into the filter’s
f
CLK
= 100kHz, f
= 100kHz, f
LTC1065, f
f
f
IN
ALIAS
= (19.6kHz, 100mV
C
= (400Hz, 3.16mV
C
= 1kHz, V
= 1kHz, V
CLK
S
S
= 5V, 1MHz SCOPE BW
2 s/DIV
= 5V, 1MHz SCOPE BW
2 s/DIV
= 20kHz, f
RMS
RMS
C
)
= 200kHz,
)
1065F08
1063 F09