LTC1565-31
7
156531fa
APPLICATIONS INFORMATION
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 voltage,
i.e., 2V for a single 5V supply and –0.5V for a ±5V supply.
Figure 6 shows the THD and SNR ratio versus 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 dif-
ferentially. For single-ended signals, connect the unused
input to Pin 3 or a common mode reference.
DIFFERENTIAL INPUT (
P-P
)
0.5
–90
THD, SNR (dB)
–80
–70
–60
–50
–30
1.0
1.5 2.0 2.5
1565-31 F05
3.0 3.5
–40
THD: V
S
= 5V, V
CM
= 2.5V
THD: V
S
= ±5V, V
CM
= 0V
SNR
f
IN
= 100kHz
Figure 5. Dynamic Range Diff-In, Diff-Out
DIFFERENTIAL INPUT VOLTAGE (V
P-P
)
0.5
–90
THD, SNR (dB)
–80
–70
–60
–50
–40
–30
1.0
1.5 2.0 2.5
1565-31 F06
3.0 3.5
THD: V
S
= 5V, V
CM
= 2V
THD: V
S
= ±5V, V
CM
= –0.5V
SNR
f
IN
= 100kHz
Figure 6. THD vs V
IN
for a Common Mode
Input Voltage 0.5V Below Mid Supply
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 specifi cations 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 fl oating Pin 7. Pin 7 can be used as an inverting
single-ended output by fl oating Pin 8. Using Pins 7 or 8
as single-ended outputs will decrease the performance.
The common mode output voltage can be adjusted by over-
driving the voltage present on Pin 3. The best performance
is achieved using a common mode output voltage that is
equal to mid supply (the default Pin 3 voltage). Figures
7 and 8 illustrate the THD versus output common mode
voltage for a 2V
P-P
differential input voltage and a common
mode input voltage that is 0.5V below mid supply.
COMMON MODE OUTPUT VOLTAGE (V)
1.51.0
THD (dB)
–50
–40
–30
3.0
4.0
1565-31 F07
–60
–70
–80
2.0 2.5 3.5
–20
–10
0
V
IN
= 2V
P-P
100kHz
V
S
= 5V
V
IN(CM)
= 2V
COMMON MODE OUTPUT VOLTAGE (V)
–4
THD (dB)
–50
–40
–30
4
1565-31 F08
–60
–70
–90
–80
–2
–3
–1 0 2
3
1
–20
–10
0
V
IN
= 2V
P-P
100kHz
V
S
= ±5V
V
IN(CM)
= –0.5V
Figure 7. THD vs Common Mode Output Voltage
Figure 8. THD vs Common Mode Output Voltage
