HFBR-0400 Datasheet, PDF (18/31 Pages) Agilent(Hewlett-Packard) – Low Cost, Miniature Fiber Optic Components with ST, SMA, SC and FC Ports

Recommended Drive
Circuits
The circuit used to supply current
to the LED transmitter can
significantly influence the optical
switching characteristics of the
LED. The optical rise/fall times
and propagation delays can be
improved by using the appro-
priate circuit techniques. The
LED drive circuit shown in
Figure 11 uses frequency com-
pensation to reduce the typical
rise/fall times of the LED and a
small pre-bias voltage to minimize
propagation delay differences
that cause pulse-width distortion.
The circuit will typically produce
rise/fall times of 3 ns, and a total
jitter including pulse-width dis-
tortion of less than 1 ns. This
circuit is recommended for appli-
cations requiring low edge jitter
or high-speed data transmission
at signal rates of up to 155 MBd.
Component values for this circuit
can be calculated for different
LED drive currents using the
equations shown below. For
additional details about LED
drive circuits, the reader is
encouraged to read Hewlett-
Packard Application Bulletin 78
and Application Note 1038.
R_y = –(V–^C––^C–-–V–^F–)––+––3–.–9–7–(–V–^C–^C––-–V–^F––-–1–.–6–V––)
I_{F ON} (A)
( ) RX1 = –1 ––R–y–
2 3.97
R_EQ2(Ω) = R_X1 - 1
R_X2 = R_X3 = R_X4 = 3(R_EQ2)
C(pF) = ^{2––0–0–0–(–p–s–)}
R_X1(Ω)
Example for I_{F ON} = 100 mA: V_F can be
obtained from Figure 9 (= 1.84 V).
R_y = –(5––-–1–.–8–4–)––+––3–.–9–7–(–5––-–1–.–8–4––- –1–.6––)
0.100
R_y = –3–.1–6––+––6–.–1–9– = 93.5 Ω
0.100
( ) RX1 = 1– –9–3–.5– = 11.8 Ω
2 3.97
R_EQ2 = 11.8 - 1 = 10.8 Ω
R_X2 = R_X3 = R_X4 = 3(10.8) = 32.4 Ω
C = ^{2–0––0–0–p––s} = 169 pF
11.8 Ω
63