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.

Signal level at various gain factor settings

Fig. 2. Signal level at various gain factor settings.

Signal level at various gain factor 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

Sample application of SU-1

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:

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