Lock-in Amplifier SU-1
The compact lock-in amplifier SU-1, developed by Tydex, is designed to amplify high-noise signals.
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.
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.
Specifications:
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
± 0,01 ÷ ± 5 V
TTL
-5 B / +10 V
Input impendence
1 MΩ
Reference acquisition time
4 s
Phase
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
high dynamic
3 μV - 100 mV RMS
Input impendence
1 MΩ
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
Output
Voltage range
± 10 V
Impendence
50 Ω
DC drift: low drift
< 50 ppm / К
high dynamic
< 500 ppm / К
Basic accuracy: ≤ 30 kHz
2 %
≥ 30 kHz
5 %
Time constants
Range
3 ms - 10 s
Filter characteristics
6 dB / octave
12 dB / octave
Dimensions and weight
Dimensions (LxHxW), mm
194х115х35
Weight, kg
5,0
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.