LTC2054CS5 查看數據表（PDF） - Linear Technology

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LTC2054CS5

Single/Dual Micropower Zero-Drift Operational Amplifi ers

Linear Technology 

LTC2054/LTC2055

APPLICATIONS INFORMATION

Clock Feedthrough, Input Bias Current

The LTC2054 and LTC2055 use auto-zeroing circuitry

to achieve an almost zero DC offset over temperature,

common mode voltage, and power supply voltage. The

frequency of the clock used for auto-zeroing is typically

1.0kHz. The term “clock feedthrough” is broadly used to

indicate visibility of this clock frequency in the op amp

output spectrum. There are typically two types of clock

feedthrough in auto-zeroed op amps like the LTC2054/

LTC2055.

The first form of clock feedthrough is caused by the settling

of the internal sampling capacitor and is input referred;

that is, it is multiplied by the closed loop gain of the op

amp. This form of clock feedthrough is independent of the

magnitude of the input source resistance or the magnitude

of the gain setting resistors. The LTC2054/LTC2055 have

an input referred residue clock feedthrough of less then

0.2μVRMS at 1.0kHz.

DC to 1Hz Noise

The second form of clock feedthrough is caused by the small

amount of charge injection occurring during the sampling

and holding of the op amp’s input offset voltage. The current

spikes are multiplied by the impedance seen at the input

terminals of the op amp, and the resulting voltage spikes

appear at the output multiplied by the closed loop gain

of the op amp. To reduce this form of clock feedthrough,

use smaller valued gain setting resistors and minimize the

source resistance at the input. If the resistance seen at the

inputs is less than 10kΩ, this form of clock feedthrough

is less than the amount of residue clock feedthrough from

the first form described above.

Placing a capacitor across the feedback resistor reduces

either form of clock feedthrough by limiting the bandwidth

of the closed loop gain.

Input bias current is defined as the DC current into the

input pins of the op amp. The same current spikes that

0.4μV

10 SEC

DC to 10Hz Noise

20545 F01

1μV

1 SEC

10

20545 F02

20545fc

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