
5
Theory
The Model 1601 photoreceiver consists of a
silicon PIN photodiode followed by a low-
noise amplifier. The Model 1611 photoreceiver
consists of an InGaAs PIN photodiode with the
same amplifier.
The 1601 photodetector has a maximum
current of 5 mA and the 1611 photodetector
has a maximum current of 10 mA. Therefore,
the maximum input optical power is 10 mW for
both detectors. The responsivity of the
photodiode is shown in Figs. 2a and 2b. Power
is delivered through a connector on the back
of the unit, and the entire package is shielded
to eliminate RF pickup. Typical frequency
responses for the Models 1601 and 1611 are
shown in Figs. 3a and 3b.
The amplifier is a low-noise, silicon amplifier
having a voltage gain of 15 and an input
impedance of 50 Ω. This unit can be
cascaded with other 50-Ω amplifiers.
Transmission lines connect the photodiode to
the amplifier and the amplifier to the output.
Microstrip transmission lines are used to
preserve speed and eliminate parasitic
inductance and capacitance that can cause
ringing. Rise time of the diode/amplifier
combination is less than 400 ps.
The AC-coupled 1601 and 1611 incorporate
blocking capacitors and a DC bias monitor
circuit as shown in Fig. 1. The corner frequency
of the high-pass filter on the AC-coupled
output is approx. 30 kHz; the corner frequency
of the low-pass filter on the DC bias monitor
output is approx. 20 kHz. The DC bias monitor
gain is 10 V/mA.