Amplified InGaAs Detector
Chapter 4: Operation
Page 4
13129-D02
Chapter 4 Operation
The PDA10DT is an amplified InGaAs photoconductive detector. The DC-coupled
amplifier circuit is designed to minimize noise.
Figure 2 Gain Control, LPF Control, and Power Selector
4.1. Output
The maximum output of the PDA10DT is 10 V for high impedance loads (
i.e.
R
LOAD
> 5 k
Ω) and 5 V for 50 Ω loads. Adjust the gain so that the measured signal level
out of the PDA10DT is below 10 V (5 V for a 50
Ω load) to avoid saturation. If
necessary, use external neutral density filters to reduce the input light level. The
BNC output signal is buffered with an amplifier capable of driving 50
Ω loads. A
50
Ω series resistor is included on the output to impedance match a 50 Ω coax
cable. For best performance, we recommend operating the PDA10DT with a 50
Ω
terminating load located at the end of the coax cable. While this is not necessary,
it eliminates ringing and distortion due to impedance mismatches.
4.2. Gain Adjustment
The PDA10DT includes a low-noise, low-offset, high-gain amplifier that allows gain
adjustment over a 70 dB range. The gain is adjusted by rotating the gain control
knob located on the side of the unit. There are 8 gain positions incremented in 10
dB steps. To adjust the gain, follow the steps below.
1. Set the gain switch to 0 dB.
2. Turn on the light source.
3. Adjust the gain setting making sure the output of the detector is below the
saturation level as indicated by section 4.1 above.
Power Toggle Switch
Gain Switch
Bandwidth
Switch
