SA5211 Datasheet, PDF (14/20 Pages) NXP Semiconductors – Transimpedance amplifier 180MHz

Philips Semiconductors
Transimpedance amplifier (180MHz)
Product specification
SA5211
60Ω then the total input capacitance, C_IN = 4 pF which will lead to
only a 12% bandwidth reduction.
NOISE
Most of the currently installed fiber-optic systems use non-coherent
transmission and detect incident optical power. Therefore, receiver
noise performance becomes very important. The input stage
achieves a low input referred noise current (spectral density) of
2.9pA/√Hz. The transresistance configuration assures that the
external high value bias resistors often required for photodiode
biasing will not contribute to the total noise system noise. The
equivalent input _RMS noise current is strongly determined by the
quiescent current of Q₁, the feedback resistor R_F, and the
bandwidth; however, it is not dependent upon the internal
Miller-capacitance. The measured wideband noise was 41nA RMS
in a 200MHz bandwidth.
DYNAMIC RANGE CALCULATIONS
The electrical dynamic range can be defined as the ratio of
maximum input current to the peak noise current:
Electrical dynamic range, D_E, in a 200MHz bandwidth assuming
I_INMAX = 60µA and a wideband noise of I_EQ=41nA_RMS for an
external source capacitance of C_S = 1pF.
D_E
+
(Max.
(Peak
input current)
noise current)
D_E(dB)
+
(60 @ 10^*6)
20 log _{(Ǹ2 41 10*9)}
D_E(dB)
+
20
log
(60mA)
(58nA)
+ 60dB
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
P
No. of incident photons/sec= _hs where P=optical incident power
l
P
No. of generated electrons/sec =
h
@
hs
l
where η = quantum efficiency
+
no.
of
generated electron hole
no. of incident photons
paris
P
NI
+
h
@
hs
l
@
e
Amps
(Coulombsńsec.)
where e = electron charge = 1.6 × 10^-19 Coulombs
h@e
Responsivity R = _hs 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
Z
+
I_EQ
qB
+
41 @ 10^*9
(1.6 @ 10^*19)(200 @ 10⁶)
+ 1281
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:
P_avMIN +
12
hc
l
B
Z
+
12 @ 2.3 @ 10^*19
200 @ 10⁶ (1281) + 719nW + * 31.5dBm
+ 1139nW + * 29.4dBm
where h is Planck’s Constant, c is the speed of light, λ is the
wavelength. The minimum input current to the SA5211, at this input
power is:
I_avMIN
+
qP
avMIN
l
hc
1
Joule
@
Joule
sec
@
q
+
I
+
707 @ 10^*9 @ 1.6 @ 10^*19
2.3 @ 10^*19
= 500nA
Choosing the maximum peak overload current of I_avMAX=60µA, the
maximum mean optical power is:
P_avMAX
+
hcI_avMAX
lq
+
2.3 @ 10^*19
1.6 @ 10^*19
60 @ 10mA
+ 86mW or * 10.6dBm (optical)
Thus the optical dynamic range, D_O is:
D_O = P_avMAX - P_avMIN = -4.6 -(-29.4) = 24.8dB.
D_O + P_avMAX * P_avMIN + * 31.5 * (* 10.6)
+ 20.8dB
1. S.D. Personick, Optical Fiber Transmission Systems,
Plenum Press, NY, 1981, Chapter 3.
OUTPUT +
A3
INPUT
A1
A2
R_F
A4
OUTPUT –
SD00327
Figure 11. SA5211 – Block Diagram
This represents the maximum limit attainable with the SA5211
operating at 200MHz bandwidth, with a half mark/half space digital
transmission at 850nm wavelength.
1998 Oct 07
14