LTC1069-6C Linear Technology, LTC1069-6C Datasheet - Page 7

• Manufacturer Part Number: LTC1069-6C
• Description: Single Supply/ Very Low Power/ Elliptic Lowpass Filter
• Manufacturer: Linear Technology

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 AGND (Pin 1) 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 in Table 2.
Table 2. Clock Feedthrough
Any parasitic switching transients during the rising and
falling edges of the incoming clock are not part of the clock
feedthrough specifications. Switching transients have fre-
APPLICATIONS
3.3V
10V
5V
V
S
– 1
– 2
– 1
– 2
2
1
0
2
1
0
1
1
V
V
V
V
S
IN
S
IN
4
3
= 5V
= SINGLE 5V
= 1.5V
= 1V
7
U
5
RMS
RMS
f
10
CUTOFF
7
FREQUENCY (kHz)
FREQUENCY (kHz)
f
CUTOFF
f
Figure 4c
Figure 4b
CLK
f
INFORMATION
13
CLK
9
U
= 20kHz
= 1MHz
CLOCK FEEDTHROUGH
= 750kHz
– 40 C
16
11
= 15kHz
– 40 C
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
13
100 V
170 V
350 V
85 C
22
15
85 C
W
25
17
RMS
RMS
RMS
1069-6 F04c
1069-6 F04a
28
19
31
21
U
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 can be reduced by adding a single RC
lowpass filter at the Output (Pin 8).
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. The frequency contents of
the wideband noise lie within the filter’s passband. The
wideband noise cannot be reduced by adding post filter-
ing. 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 specifica-
tions are not part of the wideband noise.
Table 3. Wideband Noise
Aliasing
Aliasing is an inherent phenomenon of sampled data
systems and occurs for input frequencies approaching the
sampling frequency. The internal sampling frequency of
the LTC1069-6 is 100 times its cutoff frequency. For
instance, if a 98.5kHz, 100mV
input of an LTC1069-6 operating with a 50kHz clock, a
1.5kHz, 484 V
output. Table 4 shows details.
Table 4. Aliasing (f
f
CLK
INPUT FREQUENCY
/f
98.5 (or 101.5)
99.5 (or 100.5)
(V
C
96 (or 104)
97 (or 103)
98 (or 102)
99 (or 101)
IN
= 50:1, f
3.3V
(kHz)
= 1V
V
5V
5V
S
RMS
CUTOFF
)
RMS
CLK
= 1kHz
= 50kHz)
(Relative to Input)
alias signal will appear at the filter
OUTPUT LEVEL
– 80.6
– 46.3
– 1.38
–78.3
–70.4
– 2.8
(dB)
WIDEBAND NOISE
RMS
118 V
123 V
127 V
signal is applied at the
RMS
RMS
RMS
LTC1069-6
OUTPUT FREQUENCY
(Aliased Frequency)
(kHz)
4.0
3.0
2.0
1.5
1.0
0.5
7