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

• Manufacturer Part Number: LTC1069-7
• Description: Linear Phase 8th Order Lowpass Filter
• Manufacturer: Linear Technology

APPLICATIONS
Temperature Behavior
The power supply current of the LTC1069-7 has a positive
temperature coefficient. The GBW product of its internal
op amps is nearly constant and the speed of the device
does not degrade at high temperatures.
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 the AGND pin 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 on 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-
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) of the LTC1069-7.
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. Most of the wideband
noise frequency contents lie within the filter passband.
The wideband noise cannot be reduced by adding post
filtering. The total wideband noise is nearly independent of
V
5V
5V
S
U
INFORMATION
U
CLOCK FEEDTHROUGH
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.
400 V
850 V
W
RMS
RMS
U
the clock frequency and depends slightly on the power
supply voltage (see Table 3). The clock feedthrough speci-
fications are not part of the wideband noise.
Table 3. Wideband Noise
Aliasing
Aliasing is an inherent phenomenon of sampled data
systems and it occurs for input frequencies approaching
the sampling frequency. The internal sampling frequency
of the LTC1069-7 is 50 times its f
instance if a 48kHz, 100mV
input of an LTC1069-7 operating with a 50% duty cycle
25kHz clock, a 2kHz, 741 V
the filter output. Table 4 shows details.
Table 4. Aliasing
f
Speed Limitations
To avoid op amp slew rate limiting, the signal amplitude
should be kept below a specified level as shown in Table 5.
Table 5. Maximum V
CLK
48.5kHz (or 51.5kHz)
49.5kHz (or 50.5kHz)
INPUT FREQUENCY
/f
40kHz (or 60kHz)
47kHz (or 53kHz)
48kHz (or 52kHz)
49kHz (or 52kHz)
C
5V
V
V
5V
= 25:1, f
S
IN
4.75V
= 1V
V
5V
S
RMS
CUTOFF
MAXIMUM CLOCK
= 1kHz
IN
2.5MHz
4.5MHz
vs V
Relative to Input
OUTPUT LEVEL
S
and Clock
–59.9dB
–54.2dB
–42.6dB
–18.3dB
–0.65dB
–2.9dB
RMS
RMS
WIDEBAND NOISE
alias signal will appear at
signal is applied at the
125 V
140 V
CUTOFF
340mV
1.2V
LTC1069-7
OUTPUT FREQUENCY
MAXIMUM V
Aliased Frequency
RMS
RMS
RMS
RMS
frequency. For
(f
(f
1.0kHz
IN
1.5kHz
0.5kHz
10kHz
3kHz
2kHz
IN
400kHz)
200kHz)
IN
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