AD8608 Analog Devices, AD8608 Datasheet - Page 17

• Manufacturer Part Number: AD8608
• Description: Precision, Low Noise, CMOS, Rail-to-Rail, Input/Output Operational Amplifier (Quad)
• Manufacturer: Analog Devices

Specifications of AD8608

• Vcc-vee: 2.7V to 6V
• Isy Per Amplifier: 1.2mA
• Packages: SOIC,SOP
• -3db Bandwidth: 10MHz
• Slew Rate: 5V/µs
• Vos: 20µV
• Ib: 200fA
• # Opamps Per Pkg: 4
• Input Noise (nv/rthz): 6.5nV/rtHz

Data Sheet
TOTAL NOISE INCLUDING SOURCE RESISTORS
The low input current noise and input bias current of the
AD8605
input source resistance, such as photodiodes. Input offset voltage
increases by less than 0.5 nV per 1 kΩ of source resistance at
room temperature and increases to 10 nV at 85°C. The total
noise density of the circuit is
where:
e
i
R
k is Boltzmann’s constant (1.38 × 10
T is the ambient temperature in Kelvin (T = 273 + °C).
For example, with R
roughly 15 nV/√Hz.
For R
The current noise of the
not become a significant term unless R
The total equivalent rms noise over a specific bandwidth is
expressed as
where BW is the bandwidth in hertz.
Note that the previous analysis is valid for frequencies greater
than 100 Hz and assumes relatively flat noise, above 10 kHz. For
lower frequencies, flicker noise (1/f) must be considered.
CHANNEL SEPARATION
Channel separation, or inverse crosstalk, is a measure of the signal
feed from one amplifier (channel) to another on the same IC.
The
up to frequencies of 1 MHz, allowing the two amplifiers to
amplify ac signals independently in most applications.
CAPACITIVE LOAD DRIVE
The AD860x can drive large capacitive loads without oscillation.
Figure 48 shows the output of the
200 mV input signal. In this case, the amplifier is configured
in positive unity gain, worst case for stability, while driving a
1000 pF load at its output. Driving larger capacitive loads in
unity gain can require the use of additional circuitry.
n
n
S
is the input current noise density of the AD8605.
is the input voltage noise density of the AD8605.
is the source resistance at the noninverting terminal.
AD8606
e
E
S
n
< 3.9 kΩ, e
n
,
TOTAL
=
make it the ideal amplifier for circuits with substantial
(
e
n
,
=
TOTAL
has a channel separation of greater than −160 dB
e
n
n
)
2
dominates and e
S
+
BW
= 10 kΩ, the total voltage noise density is
(
i
n
AD8605
R
S
)
2
+
4
is so low that its total density does
k
TR
AD8606
n, TOTAL
−23
S
S
is greater than 6 MΩ.
J/K).
≈ e
in response to a
n
.
Rev. L | Page 17 of 24
A snubber network, shown in Figure 49, helps reduce the signal
overshoot to a minimum and maintain stability. Although this
circuit does not recover the loss of bandwidth induced by large
capacitive loads, it greatly reduces the overshoot and ringing.
This method does not reduce the maximum output swing of the
amplifier.
–100
–120
–140
–160
–180
200mV
–20
–40
–60
–80
Figure 48.
0
100
V
IN
Figure 47. Channel Separation vs. Frequency
Figure 49. Snubber Network Configuration
AD8606
1k
2
3
Capacitive Load Drive Without Snubber
AD8605
FREQUENCY (Hz)
10k
AD8605/AD8606/AD8608
TIME (10µs/DIV)
4
8
V+
V–
100k
1
1M
C
R
V
A
R
C
S
S
V
L
L
S
= ±2.5V
= 1
= 10kΩ
= 1000pF
10M
R
L
100M
C
L