Datasheet LTC1051, LTC1053 (Analog Devices) - 8

LTC1051/LTC1053
U U W U APPLICATIO S I FOR ATIO LTC1051/LTC1053 as AC Amplifiers Aliasing
Although initially chopper stabilized op amps were de- The LTC1051/LTC1053 are equipped with internal cir- signed to minimize DC offsets and offset drifts, the cuitry to minimize aliasing. Aliasing, no matter how small, LTC1051/LTC1053 family, on top of its outstanding DC occurs when the input signal approaches and exceeds the characteristics, presents efficient AC performance. For internal sampling rate. Aliasing is caused by the sampled instance, at single 5V supply, each op amp typically data nature of the chopper op amps. A generalized study consumes 0.5mA and still provides 1.8MHz gain band- of this phenomenon is beyond the scope of a data sheet; width product and 3V/µs slew rate. This, combined with however, a set of rules of thumb can answer many almost distortionless swing to the supply rails (Figure 8), questions: makes the LTC1051/LTC1053 op amps nearly general 1. Alias signals can be generally defined as output AC purpose. To further expand this idea (the “aliasing” phe- signals at a frequency of nf nomenon) which can occur under AC conditions, should CLK ± mfIN. The nfCLK term is the internal sampling frequency of the chopper stabilized op be described and properly evaluated. amps and its harmonics; mfIN is the frequency of the input signal and its harmonics, if any. B: MAG STATUS: PAUSED RANGE: 9dBV RMS: 25 20dBV R2 10k 5V 80dB 15dB /DIV R1 0.1µF 1k 2 – 1/2 1 f V IN LTC1051 OUT 3 0.8VP-P + 50pF –100 START: 100Hz BW: 47.742Hz STOP: 5 100Hz 0.1µF X: 1825Hz Y: – 70.72dBV – 5V 1051/53 F05a fIN = 750Hz fCLK – fIN 2fIN 2fCLK – fIN
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 STATUS: PAUSED RANGE: 11dBV RMS: 25 20dBV 74dB 15dB /DIV –100 CENTER: 10 000Hz BW: 95.485Hz SPAN: 10 000Hz X: 5550Hz Y: – 63.91dBV 6fCLK – fIN fIN = 10kHz
Figure 5b. Same as Figure 5a, but the AC Input Signal is 900mV, 10kHz
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