Amplified InAsSb Detector
Chapter 4: Operation
Page 6
TTN010624-D02
4.3.
Bandwidth Filter Adjustment
The PDA10PT also includes an adjustable low-pass filter with settings from 12.5 kHz to 1600 kHz in 8 steps. This
filter allows the user to optimize the PDA10PT to operate at the lowest amount of high-frequency optical and
electrical noise. The filter is adjusted by rotating the filter control knob, located on the side of the unit. To adjust
the filter, follow the steps below:
1) Determine the maximum bandwidth required.
2) Set the filter bandwidth switch setting just above the desired bandwidth.
Note that the system signal bandwidth is 800 KHz. The 1600 KHz setting is provided to eliminate high-frequency
noise introduced above this limit.
4.4.
Thermoelectric Cooler
The thermoelectric cooler built into the detector is factory set to cool the detector to -30 °C with a thermistor
providing feedback to maintain a constant temperature. The housing is used as a heat sink and includes a fan to
increase the cooling capacity. It is important to note that the cooling fan will keep the heat sink at room
temperature. Without it, the heat sink will warm up, causing a higher temperature drop from the heat sink to the
detector element, resulting in larger TEC currents. Without the fan, the TEC current will operate at its limit (~820
mA) and the detector element will no longer be temperature stabilized. Offsets will increase and fluctuate, and
output noise will increase. For best results do not block, limit airflow to, or stop the cooling fan. This operation is
automatic and requires no input or adjustment by the user.
4.5.
Light-to-Current Conversion
The Spectral Responsivity,
(
), can be obtained from Figure 6 on page 15 to estimate the amount of output
voltage to expect. The light-to-Voltage conversion can be estimated by factoring the wavelength-dependent
responsivity of the InAsSb detector with the gain as shown below:
V
out
(V) = Gain 𝑉 𝐴
⁄ ∗ ℜ(λ) 𝐴 𝑊
⁄
∗ Input Power (W)
For terminators with low resistance, <5 kΩ or 1% error, an additional factor needs to be included in the above
formula. As described above, the output includes a 50 Ω series resistor (R
S
). The output load creates a voltage
divider with the 50 Ω series resistor as follows:
Scale Factor =
𝑅
𝐿𝑂𝐴𝐷
(𝑅
𝐿𝑂𝐴𝐷
+ 𝑅
𝑆
)
Where R
LOAD
is the terminating resistor and R
S
= 50 Ω. For a standard 50 Ω terminator, the gain will be scaled by
½ as shown below:
Scale Factor =
50 Ω
(50 Ω + 50 Ω)
= 0.5
𝑉
𝑜𝑢𝑡
(𝑉) = 𝐺𝑎𝑖𝑛 𝑉 𝐴
⁄ ∗ ℜ(𝜆) 𝐴 𝑊
⁄
∗ Input Power (W) ∗ 𝑆𝑐𝑎𝑙𝑒 𝐹𝑎𝑐𝑡𝑜𝑟
Where gain is specified in V/A and
𝕽(𝝀)
represents the responsivity in A/W.
