LTC1051/LTC1053
APPLICATIO S I FOR ATIO
2. If we arbitrarily accept that “aliasing” occurs when
output alias signals reach an amplitude of 0.01% or more
of the output signal, then: the approximate minimum
frequency of an AC input signal which will cause aliasing
is equal to the internal clock frequency multiplied by the
square root of the op amp feedback factor. For instance,
with closed-loop gain of –10, the feedback factor is 1/11
and if f
CLK
= 2.6kHz, alias signals can be detected when
the frequency of the input signal exceeds 750Hz to 800Hz
(Figure 5a).
3. The number of alias signals increases when the input
signal frequency increases (Figure 5b).
13dBV
B: MAG
RANGE: 9dBV
15dB
/DIV
–107
CENTER: 2 625Hz
X: 2535Hz
BW: 19.097Hz
Y: – 74.16dBV
f
IN
= 2.685kHz
NOTE: THE f
CLK
– f
IN
= 85Hz
ALIAS FREQUENCY IS 95dB
2f
CLK
– f
IN
DOWN FROM THE OUTPUT LEVEL
f
CLK
Figure 6a. Output Voltage Spectrum of 1/2 LTC1051 Operating as a Unity-Gain Inverting Amplifier.
V
S
=
±5V,
R
L
= 10k, C
L
= 50pF, V
IN
= 8V
P-P
, 2.685kHz
B: MAG
RANGE: 9dBV
13dBV
STATUS: PAUSED
RMS: 50
15dB
80dB
15dB
/DIV
–107
CENTER: 10 000Hz
X: 10000Hz
5f
CLK
– f
IN
f
IN
– 2f
CLK
2 • f
CLK
6f
CLK
– f
IN
NOTE: ALL ALIAS FREQUENCY
80dB TO 84dB DOWN FROM OUTPUT
Figure 6b. Output Voltage Spectrum of 1/2 LTC1051 Operating as a Unity-Gain Inverting Amplifier.
V
S
=
±5V,
R
L
= 10k, C
L
= 50pF, V
IN
= 8V
P-P
, 10kHz
10513fa
U
4. When the frequency, f
IN
, of the input signal is less than
f
CLOCK
, the alias signal(s) amplitude(s) directly scale with
the amplitude of the incoming signal. The output “signal to
alias ratio” cannot be increased by just boosting the input
signal amplitude. However, when the input AC signal
frequency well exceeds the clock frequency, the amplitude
of the alias signals does not directly scale with the input
amplitude. The “signal to alias ratio” increases when the
output swings closely to the rails. (See Figure 5b and
Figure 7.) It is important to note that the LTC1051/
LTC1053 op amps, under light loads (R
L
≥
10k), swing
closely to the supply rails without generating harmonic
distortion (Figure 8).
STATUS: PAUSED
RMS: 25
10k
5V
83.5dB
0.1µF
10k
W
U U
–
1/2
LTC1051
+
SPAN: 2 000Hz
V
IN
= 10kHz
8V
P-P
0.1µF
– 5V
50pF
1051/53 F05a
BW: 95.485Hz
Y: 7.98dBV
SPAN: 10 000Hz
1kHz
f
IN
– f
CLK
f
IN
= 10kHz
9
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