LTC1069-1
7
10691fa
APPLICATIONS INFORMATION
Temperature Behavior
The power supply current of the LTC1069-1 has a positive
temperature coeffi cient. The GBW product of its internal
op amps is nearly constant and the speed of the device
does not degrade at high temperatures. Figures 3a, 3b and
3c show the behavior of the maximum passband of the
device for various supplies and temperatures. The fi lter,
especially at ±5V supply, has a passband behavior which
is nearly temperature independent.
Clock Feedthrough
The clock feedthrough is defi ned as the RMS value of the
clock frequency and its harmonics that are present at the
fi lter’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
V
S
CLOCK FEEDTHROUGH
3.3V 10μV
RMS
5V 40μV
RMS
±5V 160μVRMS
Any parasitic switching transients during the rise and
fall edges of the incoming clock are not part of the clock
feedthrough specifi cations. Switching transients have
frequency contents much higher than the applied clock;
their amplitude strongly depends on scope probing tech-
niques as well as grounding and power supply bypassing.
The clock feedthrough can be reduced, if bothersome, by
adding a single RC lowpass fi lter at the output pin (8) of
the LTC1069-1.
Wideband Noise
The wideband noise of the fi lter 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 fi lter passband.
The wideband noise cannot be reduced by adding post
fi ltering. 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 speci
fi cations are not part of the wideband noise.
Table 3. Wideband Noise
V
S
WIDEBAND NOISE
3.3V 100μV
RMS
5V 108μV
RMS
±5V 112μV
RMS
Figure 3a Figure 3b Figure 3c
FREQUENCY (kHz)
0.5
GAIN (dB)
6.5
10691 F03a
2.5 4.5
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
1.5 3.5 5.5 7.5
V
S
= 3.3V
f
CLK
= 750kHz
V
IN
= 0.5V
RMS
T
A
= 85°C
T
A
= 25°C
T
A
= –40°C
FREQUENCY (kHz)
0.5
GAIN (dB)
6.5
10691 F03b
2.5 4.5
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
1.5 3.5 5.5 7.5 8.5 9.5 10.5
V
S
= 5V
f
CLK
= 1MHz
V
IN
= 1.2V
RMS
T
A
= 25°C
T
A
= 85°C
T
A
= –40°C
FREQUENCY (kHz)
1
GAIN (dB)
13
10691 F03c
59
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
3 7 11 15
V
S
= ±5V
f
CLK
= 1.5MHz
V
IN
= 2V
RMS
T
A
= 85°C
T
A
= –40°C
T
A
= 25°C
