LTC1051_1 Datasheet, PDF (8/16 Pages) Linear Technology – Dual/Quad Precision Zero-Drift Operational Amplifiers With Internal Capacitors

LTC1051/LTC1053
APPLICATIO S I FOR ATIO
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
signals at a frequency of nf_CLK ± mf_IN. The nf_CLK term is the
internal sampling frequency of the chopper stabilized op
amps and its harmonics; mf_IN is the frequency of the input
signal and its harmonics, if any.
B: MAG
RANGE: 9dBV
20dBV
STATUS: PAUSED
RMS: 25
R2
10k
15dB
/DIV
80dB
–100
START: 100Hz
X: 1825Hz
f_IN = 750Hz
BW: 47.742Hz
Y: – 70.72dBV
f_CLK – f_IN
2f_IN
STOP: 5 100Hz
2f_CLK – f_IN
R1
1k
f_IN
0.8V_P-P
5V
2
–
1/2
3
LTC1051
+
0.1µF
1
V_OUT
50pF
– 5V
0.1µF
1051/53 F05a
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
A: MAG
RANGE: 11dBV
20dBV
STATUS: PAUSED
RMS: 25
15dB
/DIV
74dB
8
–100
CENTER: 10 000Hz
X: 5550Hz
BW: 95.485Hz
Y: – 63.91dBV
SPAN: 10 000Hz
6f_CLK – f_IN
f_IN = 10kHz
Figure 5b. Same as Figure 5a, but the AC Input Signal is 900mV, 10kHz
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