Datasheet

LTC1051/LTC1053
8
10513fa
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.
–
+
1/2
LTC1051
1051/53 F05a
R1
1k
R2
10k
1
2
3
f
IN
0.8V
P-P
0.1µF
0.1µF
50pF
5V
–5V
V
OUT
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
f
IN
= 750Hz f
CLK
– f
IN
2f
IN
2f
CLK
– f
IN
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
f
IN
= 10kHz
6f
CLK
– f
IN
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
WUUU