LTC1565-31 Linear Technology, LTC1565-31 Datasheet - Page 6

• Manufacturer Part Number: LTC1565-31
• Description: 650kHz Continuous Time/ Linear Phase Lowpass Filter
• Manufacturer: Linear Technology

APPLICATIONS
LTC1565-31
input voltages are Pin 1 = 2.5V DC 0.5V and Pin 2 = 2.5V
DC 0.5V. Also note Figure 5 shows a 78dB SNR ratio for
higher THD levels.
As seen in Figures 3 and 4, the spurious free dynamic
range can be optimized by setting the input common mode
voltage slightly below one-half of the power supply volt-
age, i.e., 2V for a single 5V supply and – 0.5V to – 1V for a
differential input voltage level for both a single 5V supply
and a 5V supply when the common mode input voltage
is 2V and – 0.5V respectively.
For best performance, the inputs should be driven differ-
entially. For single-ended signals, connect the unused
input to Pin 3 or a common mode reference.
6
5V supply. Figure 6 shows the THD and SNR ratio versus
–30
–40
–50
–60
–80
–90
–70
–40
–80
–90
Figure 5. Dynamic Range Diff-In, Diff-Out
–50
–60
–70
Figure 6. THD vs V
Input Voltage 0.5V Below Mid Supply
0.5
0.5
f
f
IN
IN
= 100kHz
DIFFERENTIAL INPUT VOLTAGE (V
= 100kHz
1.0
1.0
THD: V
THD: V
SNR
THD: V
THD: V
SNR
U
DIFFERENTIAL INPUT (
1.5
S
S
1.5
S
S
= 5V
= 5V
= 5V
= 5V
INFORMATION
U
IN
2.0
2.0
for a Common Mode
2.5
2.5
P-P
W
)
3.0
3.0
P-P
1565-31 F05
1565-31 F06
)
3.5
3.5
U
Output Common Mode and Differential Voltage Range
The output is a fully differential signal with a common mode
level equal to the voltage at Pin 3. The specifications in the
Electrical Characteristics table assume the inputs are driven
differentially and the output is observed differentially.
However, Pin 8 can be used as a single-ended output by
simply floating Pin 7. Pin 7 can be used as an inverting
single-ended output by floating Pin 8. Using Pins 7 or 8 as
single-ended outputs will decrease the performance.
The common mode output voltage can be adjusted by
overdriving the voltage present on Pin 3. The best perfor-
mance is achieved using a common mode output voltage
that is equal to mid supply (the default Pin 3 voltage). Fig-
ures 7 and 8 illustrate the THD versus output common mode
voltage for a 2V
mode input voltage that is 0.5V below mid supply.
Figure 7. THD vs Common Mode Output Voltage
Figure 8. THD vs Common Mode Output Voltage
–10
–20
–40
–50
–60
–80
–30
–70
–10
–20
–30
–40
–50
–60
–80
–90
–70
0
0
1.5
–4
V
V
V
P-P
IN
S
IN(CM)
COMMON MODE OUTPUT VOLTAGE (V)
COMMON MODE OUTPUT VOLTAGE (V)
= 5V
= 2V
V
V
V
IN
S
IN(CM)
differential input voltage and a common
2.0
= 5V
= 2V
= 2V
P-P
–2
100kHz
= –0.5V
P-P
2.5
100kHz
0
3.0
2
3.5
1565-31 F07
1565-31 F08
4.0
4