Datasheet LTC2054, LTC2055 (Analog Devices) - 10

LTC2054/LTC2055
APPLICATIONS INFORMATION Clock Feedthrough, Input Bias Current
The second form of clock feedthrough is caused by the small amount of charge injection occurring during the sampling The LTC2054 and LTC2055 use auto-zeroing circuitry and holding of the op amp’s input offset voltage. The current to achieve an almost zero DC offset over temperature, spikes are multiplied by the impedance seen at the input common mode voltage, and power supply voltage. The terminals of the op amp, and the resulting voltage spikes frequency of the clock used for auto-zeroing is typically appear at the output multiplied by the closed loop gain 1.0kHz. The term “clock feedthrough” is broadly used to of the op amp. To reduce this form of clock feedthrough, indicate visibility of this clock frequency in the op amp use smaller valued gain setting resistors and minimize the output spectrum. There are typically two types of clock source resistance at the input. If the resistance seen at the feedthrough in auto-zeroed op amps like the LTC2054/ inputs is less than 10kΩ, this form of clock feedthrough LTC2055. is less than the amount of residue clock feedthrough from The fi rst form of clock feedthrough is caused by the settling the fi rst form described above. of the internal sampling capacitor and is input referred; Placing a capacitor across the feedback resistor reduces that is, it is multiplied by the closed loop gain of the op either form of clock feedthrough by limiting the bandwidth amp. This form of clock feedthrough is independent of the of the closed loop gain. magnitude of the input source resistance or the magnitude of the gain setting resistors. The LTC2054/LTC2055 have Input bias current is defi ned as the DC current into the an input referred residue clock feedthrough of less then input pins of the op amp. The same current spikes that 0.2μVRMS at 1.0kHz.
DC to 1Hz Noise
0.4μV 20545 F01 10 SEC
DC to 10Hz Noise
1μV 20545 F02 1 SEC 20545fc 10