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SA5212A Datasheet, PDF (12/20 Pages) NXP Semiconductors – Transimpedance amplifier 140MHz
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Philips Semiconductors
Transimpedance amplifier (140MHz)
Product specification
SA5212A
VCC1
R1
R3
R12
VCC2
R13
INPUT
Q2
Q4
Q1
Q3
+
PHOTODIODE
R2
GND1
Q15
R14
R7
R5
R4
Q16
R15
VB2
Q11
Q12
OUT–
+
OUT+
GND2
SD00328
Figure 11. Transimpedance Amplifier
R1
IC1
INPUT
IB
IIN
Q1
VIN
IF
VCC
R3
Q2
R2
Q3
VEQ3
RF
R4
SD00329
Figure 12. Shunt-Series Input Stage
DYNAMIC RANGE
The electrical dynamic range can be defined as the ratio of
maximum input current to the peak noise current:
Electrical dynamic range, DE, in a 200MHz bandwidth assuming
IINMAX = 120µA and a wideband noise of IEQ=52nARMS for an
external source capacitance of CS = 1pF.
DE
+
(Max.
(Peak
input current)
noise current)
DE(dB)
+
20
log
(120
(Ǹ2
@ 10*6)
52nA)
DE(dB)
+
(120mA)
20 log (73nA)
+ 64dB
In order to calculate the optical dynamic range the incident optical
power must be considered.
For a given wavelength λ;
Energy of one Photon = hc watt sec (Joule)
l
Where h=Planck’s Constant = 6.6 × 10-34 Joule sec.
c = speed of light = 3 × 108 m/sec
c / λ = optical frequency
No. of incident photons/sec= where P=optical incident power
P
No. of incident photons/sec = hc
l
where P = optical incident power
P
No. of generated electrons/sec =
h
@
hc
l
where η = quantum efficiency
+
no.
of
generated electron hole
no. of incident photons
paris
P
NI
+
h
@
hc
l
@
e
Amps
(Coulombsńsec.)
where e = electron charge = 1.6 × 10-19 Coulombs
h@e
Responsivity R = hc Amp/watt
l
I + P@R
Assuming a data rate of 400 Mbaud (Bandwidth, B=200MHz), the
noise parameter Z may be calculated as:1
ǒ Ǔ Z
+
IEQ
qB
+
(1.6
@
52 @ 10*9
10*19)(200
@
106)
+
1625
Amp
Amp
where Z is the ratio of RMS noise output to the peak response to a
single hole-electron pair. Assuming 100% photodetector quantum
efficiency, half mark/half space digital transmission, 850nm
lightwave and using Gaussian approximation, the minimum required
optical power to achieve 10-9 BER is:
PavMIN +
12
hc
l
B
Z
+
12
(2.3 @ 10*19)
200 @ 106 1625 + 897nW + * 30.5dBm,
where h is Planck’s Constant, c is the speed of light, λ is the
wavelength. The minimum input current to the SA5212A, at this
input power is:
IavMIN
+
qPavMIN
l
hc
+
897 @ 10*9 @ 1.6 @ 10*19
2.3 @ 10*19
= 624nA
1998 Oct 07
12
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