Rev. 14/02/2018 subject to change without notice www.first-sensor.com contact@first-sensor.com Page 2/3
Avalanche photodiode data @ 23 C
Temperature Coefficient of VBR
M = 100; = 0 V; = 905 nm
Note 1: Measurement conditions: Setup of photo current 1 nA at M = 1 and irradiated by a 880 nm, 80 nm bandwidth LED. Increase the photo
current up to 100 nA, (M = 100) by internal multiplication due to an increasing bias voltage.
Transimpedance Amplifier data @ 25 C
(Vcc = +3.0 V to 5.5 V, TA = 0°C to 70°C, 100Ω load between OUT+ and OUT-. Typical values are at TA = 25°C, Vcc = +3.3 V)
Differential, measured with 40 µA p-p signal
Maximum Differential Output Voltage
Input = 2 mA p-p with 100 differential termination
Input Referred Noise Density
Source capacitance = 0.85 pF, see note 2
Transimpedance Linear Range
Peak to peak 0.95 < linearity < 1.05
Power Supply Rejection Ratio (PSRR)
Output referred, f < 2 MHz, PSSR = -20 Log (ΔVout / ΔVcc)
Note 2: Source capacitance for AD500-9-400M-TO5 is the capacitance of APD.
Note 3: Input referred noise is calculated as RMS output noise/ (gain at f = 10 Mhz). Noise density is (input referred noise)/√bandwidth.
Transfer Characteristics
The circuit used is an avalanche photodiode directly coupled to a high speed data handling transimpedance amplifier. The output of the APD (light generated
current) is applied to the input of the amplifier. The amplifier output is in the form of a differential voltage pulsed signal.
The APD responsivity curve is provided in Fig. 2. The term Amps/Watt involves the area of the APD and can be expressed as Amps/mm2/Watts/mm2, where
the numerator applies to the current generated divided by the area of the detector, the denominator refers to the power of the radiant energy present per
unit area. As an example assume a radiant input of 1 microwatt at 905 nm. The APD’s corresponding responsivity is 0.58 A/W.
If energy in = 1 µW, then the current from the APD = (0.58 A/W) x (1x10-6W) = 0.58 µA. We can then factor in the typical gain of the APD
of 100, making the input current to the amplifier 58 µA. From Fig. 5 we can see the amplifier output will be approximately 100 mV p-p.
Application notes
The AD500-9-400M-TO5 is a high speed optical data receiver. It incorporates an internal transimpedance amplifier with an avalanche photodiode.
This detector requires +3.5 V to +5.0 V voltage supply for the amplifier and a high voltage supply (100-240 V) for the APD. The internal APD follows the gain
curve published for the AD500-9-TO52-S1 avalanche photodiode. The transimpedance amplifier provides differential output signals in the range of 200
millivolts differential.
In order to achieve highest gain, the avalanche photodiode needs a positive bias voltage (Fig. 1). However, a current limiting resistor must be placed in series
with the photodiode bias voltage to limit the current into the transimpedance amplifier. Failure to limit this current may result in permanent failure of the
device. The suggested initial value for this limiting resistor is 390 KOhm.
When using this receiver, good high frequency placement and routing techniques should be followed in order to achieve maximum frequency response. This
includes the use of bypass capacitors, short leads and careful attention to impedance matching. The large gain bandwidth values of this device also demand
that good shielding practices be used to avoid parasitic oscillations and reduce output noise.