ADA4806-1ARJZ-R7 datasheet(19/24 Pages) AD

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Data Sheet

ADA4806-1

Rev. A | Page 19 of 24

Table 8 summarizes the threshold voltages for the

SHUTDOWN and SLEEP pins for various supplies. Table 9

shows the truth table for the SHUTDOWN and SLEEP pins.

Table 8. Threshold Voltages for Enabled Mode and

Shutdown/Sleep Modes

Mode

+3 V

+5 V

±5 V

+7 V/−2 V

Enabled

>+1.1 V

>+1.9 V

>−0.9 V

>+1.6 V

Shutdown/Sleep

Mode

<+0.7 V

<+1.5 V

<−1.3 V

<+1.2 V

Table 9. Truth Table for the SHUTDOWN and SLEEP Pins

SHUTDOWN

SLEEP

Operating State

Low

Powered down

Low

High

Powered down

High

Low

Low power mode

High

Full power mode

NOISE CONSIDERATIONS

Figure 55 shows the primary noise contributors for the typical

gain configurations. The total output noise (vn_OUT) is the root

sum square of all the noise contributions.

in–

4kTRS

Vn_RS =

4kTRG

Vn_RG =

Vn_RF =

+ Vn_OUT

4kTRF

in+

Figure 55. Noise Sources in Typical Connection

The output noise spectral density is calculated by

[

]

OUT

kTR

kTRs

kTR

−

























where:

k is Boltzmann’s constant.

T is the absolute temperature in degrees Kelvin.

RF and RG are the feedback network resistances, as shown in

Figure 55.

RS is the source resistance, as shown in Figure 55.

in+ and in− represent the amplifier input current noise spectral

density in pA/√Hz.

vn is the amplifier input voltage noise spectral density in

nV/√Hz.

Source resistance noise, amplifier input voltage noise (vn), and

the voltage noise from the amplifier input current noise

(in+ × RS) are all subject to the noise gain term (1 + RF/RG).

Figure 56 shows the total referred to input (RTI) noise due to

the amplifier vs. the source resistance. Note that with a

5.9 nV/√Hz input voltage noise and 0.6 pA/√Hz input current

noise, the noise contributions of the amplifier are relatively

small for source resistances from approximately 2.6 kΩ to

47 kΩ.

The Analog Devices, Inc., silicon germanium (SiGe) bipolar

process makes it possible to achieve a low noise of 5.9 nV/√Hz

for the ADA4806-1. This noise is much improved compared to

similar low power amplifiers with a supply current in the range

of hundreds of microamperes.

100

1000

100

10k

100k

SOURCE RESIST

ANCE (Ω)

TOTAL NOISE

SOURCE RESISTANCE NOISE

AMPLIFIER NOISE

SOURCE RESIST

ANCE = 2.6kΩ

SOURCE RESIST

ANCE = 47kΩ

Figure 56. RTI Noise vs. Source Resistance

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