AD1582/AD1583/AD1584/AD1585

–11–

REV. D

AC PERFORMANCE

To apply the AD1582/AD1583/AD1584/AD1585 family of

references, it is important to understand the effects of dynamic

output impedance and power supply rejection. In Figure 8a, a

voltage divider is formed by the AD1582’s output impedance and

by the external source impedance. Figure 8b shows the effect of

varying the load capacitor on the reference output. Power supply

rejection ratio (PSRR) should be determined when characterizing

the ac performance of a series voltage reference. Figure 9a shows a

test circuit used to measure PSRR, and Figure 9b demonstrates

the AD1582’s ability to attenuate line voltage ripple.

2

10k

10k

2V

100 A

10k

2k

5V

5 F

1 F

DUT

1

Figure 8a. Output Impedance Test Circuit

100

1

0.1

10

FREQUENCY (Hz)

10

100

1k

10k

100k

1M

1 F CAP

AD1585

AD1582

Figure 8b. Output Impedance vs. Frequency

5V

100mV

0.22 F

DUT

0.22 F

10V

10k

10k

200mV

1

Figure 9a. Ripple Rejection Test Circuit

FREQUENCY (Hz)

100

90

0

11M

10

100

1k

10k

100k

50

20

80

70

60

40

30

10

AD1582

AD1585

Figure 9b. Ripple Rejection vs. Frequency

NOISE PERFORMANCE AND REDUCTION

The noise generated by the AD1582 is typically less than

70

µV p-p over the 0.1 Hz to 10 Hz frequency band. Figure 10

shows the 0.1 Hz to 10 Hz noise of a typical AD1582. The noise

measurement is made with a high gain band-pass filter. Noise in

a 10 Hz to 10 kHz region is approximately 50

µV rms. Figure 11

shows the broadband noise of a typical AD1582. If further noise

reduction is desired, a 1-pole low-pass filter may be added

between the output pin and the ground. A time constant of 0.2 ms

has a –3 dB point at roughly 800 Hz, and reduces the high

frequency noise to about 16

µV rms. It should be noted,

however, that while additional filtering on the output may improve

the noise performance of the AD1582/AD1583/AD1584/AD1585

family, the added output impedance could degrade the ac

performance of the references.

100

90

10

0%

10 V

1s

Figure 10. 0.1 Hz to 10 Hz Voltage Noise

10

0%

100

90

10ms

100 V

Figure 11. 10 Hz to 10 kHz Wideband Noise