AD1580

Rev. F | Page 8 of 12

NOISE PERFORMANCE AND REDUCTION

The noise generated by the AD1580 is typically less than

5 µV p-p over the 0.1 Hz to 10 Hz band. Figure 17 shows the

0.1 Hz to 10 Hz noise of a typical AD1580. Noise in a 10 Hz to

10 kHz bandwidth is approximately 20 μV rms (see Figure 18a).

If further noise reduction is desired, a 1-pole low-pass filter can

be added between the output pin and ground. A time constant

of 0.2 ms has a −3 dB point at about 800 Hz and reduces the

high frequency noise to about 6.5 μV rms (see Figure 18b).

A time constant of 960 ms has a −3 dB point at 165 Hz and

reduces the high frequency noise to about 2.9 μV rms (see

Figure 18c).

1s/DIV

1µV/DIV

4.5µV p-p

Figure 17. 0.1 Hz to 10 Hz Voltage Noise

40µV/DIV

21µV rms

20µV/DIV

10µV/DIV

10ms/DIV

6.5µV rms,

τ = 0.2ms

(a)

(b)

(c)

2.90µV rms,

τ = 960ms

Figure 18. Total RMS Noise

TURN-ON TIME

Many low power instrument manufacturers are becoming

increasingly concerned with the turn-on characteristics of

components being used in their systems. Fast turn-on compo-

nents often enable the end user to keep power off when not

needed, and yet those components respond quickly when

the power is turned on for operation. Figure 19 displays the

turn-on characteristic of the AD1580.

Upon application of power (cold start), the time required for

the output voltage to reach its final value within a specified

error is the turn-on settling time. Two components normally

associated with this are time for active circuits to settle and time

for thermal gradients on the chip to stabilize. This characteristic

is generated from cold start operation and represents the true

turn-on waveform after power-up. Figure 21 shows both the

coarse and fine turn-on settling characteristics of the device;

the total settling time to within 1.0 mV is about 6 µs, and there

is no long thermal tail when the horizontal scale is expanded to

2 ms/div.

250mV/DIV

5µs/DIV

0V

2.4V

Figure 19. Turn-On Response Time

+

–

Figure 20. Turn-On, Settling, and Transient Test Circuit

Output turn-on time is modified when an external noise

reduction filter is used. When present, the time constant

of the filter dominates overall settling.

0V

2.4V

OUTPUT ERROR

1mV/DIV, 2µs/DIV

OUTPUT

0.5mV/DIV, 2ms/DIV

Figure 21. Turn-On Settling