LTC1051/LTC1053

8

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LTC1051/LTC1053 as AC Amplifiers

Although initially chopper stabilized op amps were de-

signed to minimize DC offsets and offset drifts, the

LTC1051/LTC1053 family, on top of its outstanding DC

characteristics, presents efficient AC performance. For

instance, at single 5V supply, each op amp typically

consumes 0.5mA and still provides 1.8MHz gain band-

width product and 3V/µs slew rate. This, combined with

almost distortionless swing to the supply rails (Figure 8),

makes the LTC1051/LTC1053 op amps nearly general

purpose. To further expand this idea (the “aliasing” phe-

nomenon) which can occur under AC conditions, should

be described and properly evaluated.

Aliasing

The LTC1051/LTC1053 are equipped with internal cir-

cuitry to minimize aliasing. Aliasing, no matter how small,

occurs when the input signal approaches and exceeds the

internal sampling rate. Aliasing is caused by the sampled

data nature of the chopper op amps. A generalized study

of this phenomenon is beyond the scope of a data sheet;

however, a set of rules of thumb can answer many

questions:

1. Alias signals can be generally defined as output AC

internal sampling frequency of the chopper stabilized op

signal and its harmonics, if any.

–

+

1/2

LTC1051

1051/53 F05a

R1

1k

R2

10k

1

2

3

0.1µF

0.1µF

50pF

5V

–5V

B: MAG

RANGE: 9dBV

STATUS: PAUSED

RMS: 25

20dBV

15dB

/DIV

–100

START: 100Hz

X: 1825Hz

BW: 47.742Hz

Y: – 70.72dBV

STOP: 5 100Hz

80dB

A: MAG

RANGE: 11dBV

STATUS: PAUSED

RMS: 25

20dBV

15dB

/DIV

–100

CENTER: 10 000Hz

X: 5550Hz

BW: 95.485Hz

Y: – 63.91dBV

SPAN: 10 000Hz

74dB

Figure 5a. Output Voltage Spectrum of 1/2 LTC1051 Operating as an Inverting Amplifier with Gain of 10,

and Amplifying a 750Hz/800mV, Input AC Signal

Figure 5b. Same as Figure 5a, but the AC Input Signal is 900mV, 10kHz

APPLICATIO S I FOR ATIO