Datasheet > AD823A_12

AD823A_12

更新时间： 2022-10-09 09:18:41

品牌	Logo	应用领域
亚德诺 - ADI		/
页数	文件大小	规格书
20页	509K
描述
Wide Supply Dual, 17 MHz, Rail-to-Rail

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AD823A_12 数据手册

AD823A

Data Sheet

Table 8. RMS Noise Contributions of Photodiode Preamp

Contributor

Expression

(μV)¹

R_F

55.17

4kT  R_F f_N



V_NOISE

138.5

149.1



C_S C_M C_F 2C_D



V_NOISE



 f_N

C_F

RSS Total

¹RMS noise with R_F= 50 kΩ, C_S= 5 pF, C_F= 1.2 pF, C_M= 1.3 pF, and C_D= 0.6 pF.

Figure 47 shows the two-pole Butterworth active filter’s response.

Note that it has a maximally flat pass band, a −3 dB bandwidth

of 1 MHz, and a 12 dB/octave roll-off in the stop band.

ACTIVE FILTER

The AD823A is an ideal candidate for an active filter because of

its low input bias current and its low input capacitance. Low

input bias current reduces dc error in the signal path while low

input capacitance improves the accuracy of the active filter.

The cutoff frequency (f_c) and the Q factor of the Butterworth

filter can be calculated by:

As a general rule of thumb, the bandwidth of the amplifier should

be at least 10 times bigger than the cutoff frequency of the filter

implemented. Therefore, the AD823A is capable of implementing

active filters of up to 1.7 MHz.

(7)

(8)

f_c

2 R₁R₂C₁C₂

200pF

R₁R₂C₁C₂

Q 



R₁ R₂



C₂

Therefore, one can easily adjust the cutoff frequency by

appropriately factoring the resistor and capacitor values. For

example, a 100 kHz filter can be implemented by increasing the

values of R1 and R2 by 10 times. Note that the Q factor remains

the same in this case.

1.12kΩ 1.12kΩ

100pF

49.9Ω

AD823A

OUT

–V

Figure 46. Two-Pole Sallen-Key Active Filter

Figure 46 shows an example of a second-order Butterworth

filter, which is implemented by the Sallen-Key topology. This

structure can be duplicated to produce higher-order filters.

–3

–6

–9

–12

–15

–18

–21

–24

–27

–30

–33

–36

100

10k

100k

10M

FREQUENCY (Hz)

Figure 47. Two-Pole Butterworth Active Filter Response

Rev. B | Page 18 of 20

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