Analog Devices AD620, C1599c07 specifications Ground Returns for Input Bias Currents

AD620

GROUND RETURNS FOR INPUT BIAS CURRENTS

Input bias currents are those currents necessary to bias the input transistors of an amplifier. There must be a direct return path for these currents; therefore, when amplifying “floating” input

	+VS
– INPUT
RG	AD620	VOUT
		LOAD
+ INPUT		REFERENCE
	–V
	S
		TO POWER
		SUPPLY
		GROUND

Figure 42a. Ground Returns for Bias Currents with Transformer Coupled Inputs

sources such as transformers, or ac-coupled sources, there must be a dc path from each input to ground as shown in Figure 42. Refer to the Instrumentation Amplifier Application Guide (free from Analog Devices) for more information regarding in amp applications.

+VS

– INPUT

RG	AD620	VOUT
		LOAD
+ INPUT		REFERENCE
	–V
	S
		TO POWER
		SUPPLY
		GROUND

Figure 42b. Ground Returns for Bias Currents with Thermocouple Inputs

		+VS
	– INPUT
	RG	AD620	VOUT
			LOAD
	+ INPUT		REFERENCE
100kV	100kV	–V
		S
			TO POWER
			SUPPLY
			GROUND

Figure 42c. Ground Returns for Bias Currents with AC Coupled Inputs

REV. E –15–