AD8014ART-EBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
AD8014ART-EBZ Datasheet PDF : 11 Pages
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AD8014
Figure 19. Large Signal Step Response; VS = ±5 V,
VO = 4 V Step
Figure 21 shows the circuit that was used to imitate a photo-
diode preamp. A photodiode for this application is basically a
high impedance current source that is shunted by a small ca-
pacitance. In this case, a high voltage pulse from a Picosecond
Pulse Labs Generator that is ac-coupled through a 20 kΩ resis-
tor is used to simulate the high impedance current source of a
photodiode. This circuit will convert the input voltage pulse into
a small charge package that is converted back to a voltage by the
AD8014 and the feedback resistor.
In this case the feedback resistor chosen was 1.74 kΩ, which is a
compromise between maintaining bandwidth and providing
sufficient gain in the preamp stage. The circuit preserves the
pulse shape very well with very fast rise time and a minimum of
overshoot as shown in Figure 22.
0.1F
INPUT
20k⍀
49.9⍀
1.74k⍀
+5V
AD8014
49.9⍀
OUTPUT
(10؋ PROBE)
(NO LOAD)
–5V
Figure 21. AD8014 as a Photodiode Preamp
TEK RUN: 2.0GS/s ET AVERAGE
T[ ]
Figure 20. Large Signal Step Response; VS = +5 V,
VO = 2 V Step
Note: On Figures 19 and 20 RF = 500 Ω, RS = 50 Ω and CL =
20 pF.
APPLICATIONS
CD ROM and DVD Photodiode Preamp
High speed Multi-X CD ROM and DVD drives require high
frequency photodiode preamps for their read channels. To mini-
mize the effects of the photodiode capacitance, the low imped-
ance of the inverting input of a current feedback amplifier is
advantageous. Good group delay characteristics will preserve the
pulse response of these pulses. The AD8014, having many ad-
vantages, can make an excellent low cost, low noise, low power,
and high bandwidth photodiode preamp for these applications.
INPUT 1
20V/DIV
OUTPUT 2
500mV/DIV
CH1 20.0V
CH2 500mV M 25.0ns CH4 380mV
Figure 22. Pulse Response
–8–
Rev. C
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