9

LTC1051/LTC1053

10513fa

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

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).

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/

closely to the supply rails without generating harmonic

distortion (Figure 8).

B: MAG

RANGE: 9dBV

STATUS: PAUSED

RMS: 25

13dBV

15dB

/DIV

–107

CENTER: 2 625Hz

X: 2535Hz

BW: 19.097Hz

Y: – 74.16dBV

SPAN: 2 000Hz

83.5dB

–

+

1/2

LTC1051

1051/53 F05a

10k

10k

0.1µF

0.1µF

50pF

5V

–5V

ALIAS FREQUENCY IS 95dB

DOWN FROM THE OUTPUT LEVEL

Figure 6b. Output Voltage Spectrum of 1/2 LTC1051 Operating as a Unity-Gain Inverting Amplifier.

Figure 6a. Output Voltage Spectrum of 1/2 LTC1051 Operating as a Unity-Gain Inverting Amplifier.

B: MAG

RANGE: 9dBV

STATUS: PAUSED

RMS: 50

13dBV

15dB

/DIV

–107

CENTER: 10 000Hz

X: 10000Hz

BW: 95.485Hz

Y: 7.98dBV

SPAN: 10 000Hz

80dB

15dB

1kHz

NOTE: ALL ALIAS FREQUENCY

80dB TO 84dB DOWN FROM OUTPUT

APPLICATIO S I FOR ATIO