Lock-in Amplifier SU-1

Download Lock-in Amplifier Datasheet (PDF, 458 KB)
 The compact lock-in amplifier SU-1, developed by Tydex, is designed to amplify high-noise signals.

Lock-in Amplifier SU-1

It is a homodyne detector with a low pass filter. An external reference signal is required to operate SU-1. All operating parameters (amplification, time constant and phase) are manually adjustable. Also this detector is used to measure phase shift of the signal. Schematic diagram of the detector SU-1 is provided in fig. 1.

SU-1 schematic diagram

Fig. 1. SU-1 schematic diagram.

The principle of operation of SU-1 is based on orthogonality of two sinusoidal functions. When a product of two sinusoidal functions with non-matching frequencies f1 and f2 is integrated over time well above their periods, the result is zero. On the other hand, when f1 = f2, and both functions are in phase, integrated average is equal to half of the product of the functions’ amplitudes.

SU-1 multiplies input signal to reference signal (from built-in generator or external source) and integrates the product over specified time (usually from milliseconds to a few seconds). The result is a DC signal, and the effect of any other signal not matched by frequency to the reference is dampened to almost zero. Same-frequency component that is not in phase with the reference signal is attenuated too (since same-frequency sinusoidal and cosinusoidal waves are orthogonal).

SU-1 is to be used to amplify high-noise signal produced by the following means of detecting of THz radiation: electro-optical detection of pulsed THz radiation and of detection of THz radiation using the following detectors: Golay detectors, cooled bolometers, pyro-electric THz radiation detectors, semiconductor THz radiation detectors, novel THz radiation detectors.

The figures 2 and 3 respectively show the signal dependence on SU-1  gain factor and time constant. This signal is a temporal shape  of  THz impulse obtained by EOD.

TYDEX SU-1: Signal level at various gain factor settings
Fig.2. Signal level at various gain factor settings.

TYDEX SU-1: Signal level at various time constant settings
Fig. 3. Signal level at various time constant settings


Absolute Maximum Ratings
Signal input AC voltage, V 20
Signal input DC voltage, V +/-30
Reference input voltage, V +/-15
Power supply voltage, V +/-15
Key Specifications 
Frequency range 0,01 ÷ 250 kHz
Reference Input
Signal range: bipolar ±0,1 ÷ ±5V
Signal range:TTL -5B / +10V
Input impedance  1MΩ
Reference acquisition time  4 s
Range 0 ÷ 340° 
Resolution 8 bit
Drift 0,01° / К
Accuracy ±1 bit
Voltage Input
Maximum input voltage  ±15 V
Range: low drift 30 μV - 100 mV RMS
Range:  high dynamic 3 μV - 100 mV RMS
Input impendance  1MΩ
Input voltage noise  12 nV / √Hz @ 1 kHz
Gain drift  < 100 ppm / К
Dynamic reserve
Low drift  26 dB (min)
High dynamic  46 dB (min)
Maximum dynamic  50 dB 
Voltage range  ±10 V
Impendance  50 Ω
DC drift: low drift  < 50 ppm / К
DC drif:  high dynamic  < 500 ppm / К
Basic accuracy: low drift ≤ 30 kHz  2 %
Basic accuracy: high dynamic ≥ 30 kHz 5 %
Time constants
Range  3 ms ÷ 10 s
Filter characteristics: low drift 6 dB / octave
Параметры фильтр  high dynamic 12 dB / octave
Dimensions (L x H x W), mm 194 x 115 x 35
Weight, kg 5.0

SU-1 within THz radiation detector  based on THz scanning Fabry-Perot interferometer with Golay Detector

Fig. 4. Sample application of SU-1 within THz radiation detector based on
THz scanning Fabry-Perot interferometer with Golay Detector

Key features:

  • Operating frequency up to 250 KHz;  
  • Adjustable sensitivity, time constant and phase;
  • Compact and EMI (electromagnetic interference) shielded enclosure.

SU-1 package includes 

  • electronic unit,
  • power supply,
  • 3 RF-connector cables (1.5 m each),
  • operating mannual.

Following accessories for SU-1 can be supplied separatly:

For quotation and delivery please fill in our request form.