Terahertz Technologies Inc.Terahertz Technologies Inc.
(888) U.S.-OTDRS
PDA-750 Photodiode Transimpedance Amplifier

The PDA-750 is a low noise, high gain, transimpedance amplifier designed to provide a direct digital readout of the current generated from a photodiode photomultiplier, or other similar current source. With full scale input ranges of ± 20 nA to ± 20 mA and a noise level of less than 1 pA, the PDA-750 offers superb dynamic range.

Digital entry of an Amps/Watt setting via the front panel controls permits the instrument to display current measurements in units of Watts. The A/W setting ranges from 1.000 to 0.100.

A variable bias supply is built into the instrument and may be switched into series with the device under test. It can supply digitally selectable voltages ranging from -14.00 to + 14.00 volts.

The Offset control permits the nulling of background signals as large as ± 200% of the range currently in use.

Rechargeable batteries isolate the unit from the mains and eliminate the effects of ground loops and/or power line noise that may be present during sensitive measurements. They will power the instrument for approximately 10 hours between charges. The unit may be operated normally while the batteries are charging.

The large 4 1/2 digit Liquid Crystal Display provides a maximum resolution of 1 part in ± 20,000, thus enabling the detection of very small changes in the signal under test.

An analog output port provides a ± 2 Volt full-scale signal that is directly proportional to the display reading of ± 20,000 counts.

The PDA-750 is equipped with a bi-directional Rs-232 serial port that enables the user to remotely control the instrument and read data and the instrument’s status.

Applications for the PDA-750 include: serving as a precision readout device for Unity Quantum Efficient detectors such as the QED-150 manufactured by UDT Instruments, characterization of detector dark current, a readout interface for spectrometers, spectral calibration of detectors, a high gain precision transimpedance  amplifier and as a sensitive, high precision optical power meter.

The ease of use and convenience of this instrument is typical of TTI products. This instrument is covered by our standard 2 year limited warranty and 30 day guarantee of satisfaction.

Eight Decade Dynamic Range
Less Than 1 pA Noise
Maximum Resolution 1 part in +/- 20 000
Rechargeable Ni-mH Batteries for Low Noise
Digital Input of A/W Value Yields Readout in Watts
Computer Interface for Easy Control
Background Cancelation of +/- 200 %
Digitally Set Bias Source from -14.00V to +14.00V

Ordering Information


Photodiode Amplifier


Photodiode Amplifier and 10DP Si Photodiode with Stand and Holder


10DP Si Photodiode with Stand and Holder

 PDA-750 Photodiode Amplifier Specifications

Full Scale Ranges

± 20 nA to ± 20 mA in decade steps, 1 pA maximum resolution

Maximum Input Current Without Damage

±  25 mA

Measurement Uncertainty

± 0.05 % of Reading ± 2 Least Significant Digits

A/W Setting

0.100 to 1.000 A/W in increments of .005 A/W

Input Impedance (DC to 2 KHz)

Zero Ohms Virtual Ground, Single Ended

Input Capacitance

25 pF

Output Impedance

100 Ohms

Bias Voltage

Selectable from - 14 V to + 14 V in 6.5 mv increments

Analog Output Port

± 2 V corresponds to ± 20 000 counts of range in use

Noise and Drift

< ± 1 pA/5 seconds on most sensitive range

Background Cancellation

± 200 % of the range in use

Analog Output Port Frequency Response

DC to 2 KHz, most sensitive range

DC to 40 KHz, least sensitive range

Rs-232 Interface

9600 Baud, N-8-1, 3 wire, Bi-directional, Cable Provided


4 1/2 Digit LCD, 0.4" high

Power Requirements

Rechargeable Ni-mH batteries provide approximately 10 hours of use

External Power Supply/Charger

85 - 250 VAC, 50-60 Hz, < 9 VA

Mains Adaptors

Adaptors provided for US, Continental Europe, Great Britain and Australia 

Operating Temperature Range

0° to 40°C


5.5" W x 2.5” H x 8.5” L  (140 x 63 x 215 mm)


2 Lbs., 0.9 kg (excluding external power supply)

Interconnecting cable supplied

Rs-232, 14 feet max length

CE Certification


Accessories Provided

Rs-232 cable, Power Supply/Charger, Operating Manual

Standard Warranty

Two years, Components and Workmanship

30 Day Satisfaction Guarantee

Application Software Provided

Downloadable from TTI Website


 PIN 10DP Photovoltaic Detector

Active Area

Area (mm2) 100, Dimensions (mm) 11.28ᶲ

Peak Responsivity Wavelength typ. (λp)


Responsivity at λp

Min. 0.55 A/W and typ. 0.60 A/W

Capacitance (pF) OV

9800 Max.

Shunt Resistance (GΩ at -10mV)

Min. 0.05 A/W and Typ. 0.2 A/W

NEP @ 0V and 970nm

6.8 3-15 typ.

Rise Time @ 0V and 632nm with 50Ω

1000 ns typ.

Temp range

 Operating -40°C to 100°C, Storage -55°C to 125°C

Data Sheet
PDA-750 Data Sheet
PDA-750 Manual
Software Download

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