Two-channel synchronous amplifier SpectraLIA

The SOL instruments SpectraLIA is a high performance two-channel single phase analog Lock-in amplifier. In combination with a PhaseLocked Chopper, it can detect the useful periodic signals with a predefined frequency against the strong background noise, the magnitude of which can exceed the amplitude of the useful signal by tens or hundreds of times.

The use of a lock-in amplifier can significantly improve the signal-to-noise ratio when detecting extremely low signals. For example, it can be used to detect signals from the single-element infrared detectors having usually low sensitivity and weak output signals.

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Description of the lock-in amplifier SpectraLIA

Two-channel synchronous amplifier SpectraLIA

Two-channel Lock-in amplifier SpectraLIA allows independent settings of the signal acquisition parameters for two different single-channel detectors, simultaneously installed at the output ports of the SOL instruments spectral devices.

The SpectraLIA use phase-sensitive detection techniques to separate the signal from the noise sources. Detection is achieved by using a reference signal at a specific frequency and comparing it to the detected signal as a multiplication function – unless the reference and signal frequencies are identical, the average of the product is zero. The phasesensitive detector (PSD) performs the multiplication as part of the lock-in amplifier, driving the noise to zero and singling out the frequency of the signal. The amplifier adjusts the gain of the incoming signal, then using the PSD multiplies it by the internal lock-in reference signal. The output signal passes through a low pass filter, which removes the ac signals, leaving a dc signal that is proportional to the initial signal amplitude. Lock-in amplifiers greatly improve the signal-to-noise ratio of a system.

The SpectraLIA consists of two independent identical lock-in amplifiers and one chopper, which forms a reference signal for controlling both lock-in amplifiers. The chopper is unambiguously installed directly on the entrance slit of the spectral devices manufactured by SOL instruments, and it does not require any adjustment.

The SpectraLIA can be optionally delivered with an additional low-noise power supply to use it with the detectors from other producers.

Block diagram of the SpectraLIA

Block diagram of the lock-in amplifier SpectraLIA

SpectraLIA includes:

  • Signal Amplifier with a Low noise differential amplifier

  • Multiplier, i.e. the phase sensitive detector (PSD)

  • Low-pass filter
  • DC amplifier
  • Chopper

Definitions of components of the SpectraLIA amplifier

The signal to be measured is fed into the input of the Signal Amplifier. The output of the DC amplifier is a DC voltage proportional to measured voltage. This voltage is available at the output connector.

The Signal amplifier is an AC voltage amplifier, which includes a low-noise instrumental  differential amplifier, precision amplifier with selectable gain and a bandpass filter. The gain is set using the switch installed on the front panel. Gain 1, 10, 100 and 1000 can be set to provide a wide range of input signal levels. The bandpass filter cuts off signals with frequencies below 150 Hz, including the main and double frequency of the mains voltage, as well as signals with frequencies above 1200 Hz to reduce noise in the measured signal.

The phase sensitive detector PSD is a circuit which takes in two voltages as inputs Vsignal and Vreference and produces an output which is the product Vsignal * Vreference. That is, the PSD is a multiplier circuit.

The low pass filter is a higher-order active low-pass “many pole” filter whose time constant may be selected. The time constant is set using the switch installed on the front panel.

The DC amplifier is a low-frequency amplifier with selectable gain. It differs from the Signal Amplifier in that it works all the way down to zero frequency (DC) and is not intended to work well at frequencies above 10 KHz. Gain 1, 2, 4 and 8 can be set.

The Chopper is designed to modulate an optical signal at the input of a spectral instrument. The Chopper Controller sets the modulation frequency and maintains it with high accuracy using an optical sensor. The Chopper Controller also generates a reference signal for both lock-in amplifiers.

Specification of two-channel lock-in amplifier SpectraLIA

Signal сhannel
Inputs:Voltage Single-ended
Impedance:100 kΩ + 30 pF, AC coupled
Full-scale sensitivity:from 0.5 μV to 1 V
Noise:4 nV/√Hz at 500 Hz (typ.)
Pre gain:1, 10, 100, 1000
Post gain:1, 2, 4, 8
Demodulator and output signal
Stability:50 ppm/°C
Time constant:10, 50, 100, 500, 1000 ms
Dynamic range:typically > 80 dB
SNR:typically > 60 dB
Measurement accuracy:< 0.1% (150-1000 Hz)
Maximum output voltage / current:10 V / 10 mA

Signal сhannel

  • Inputs: Voltage Single-ended

  • Impedance: 100 kΩ + 30 pF, AC coupled

  • Full-scale sensitivity: from 0.5 μV to 1 V

  • Noise: 4 nV/√Hz at 500 Hz (typ.)
  • Pre gain: 1, 10, 100, 1000

  • Post gain: 1, 2, 4, 8

Demodulator and output signal

  • Stability: 50 ppm/°C

  • Time constant: 10, 50, 100, 500, 1000 ms
  • Dynamic range: greater than 80 dB (typically)
  • SNR: greater than 60 dB (typically)
  • Measurement accuracy: less than 0.1% (150-1000 Hz)
  • Maximum output voltage / current: 10 V / 10 mA
Disk diameter:120 mm
Aperture:9 mm
Frequency range:150-1400 Hz
Motor:DС current with optical encoder
Mounting:couples directly to SOL instruments monochromator entrance slit assemblies
Input and output connectors:BNC
Power:100…240 VAC, <10W
Low-noise power supply for powering third-party`s detectors
Output voltage:± 15 V
Output current:± 100 mA max
Regulation:0.05 % network & load
Ripple:0.5 mV RMS max output
Connections:9-pin DB-Socket connector


  • Disk diameter: 120 mm
  • Aperture: 9 mm

  • Frequency range: 150-1400 Hz
  • Motor: DС current with optical encoder
  • Mounting: couples directly to SOL instruments monochromator entrance slit assemblies

General characteristics

  • Input and output connectors: BNC
  • Power: 100… 240 VAC, <10 W

Low-noise power supply for powering Electro-Optical Systems’ receivers

  • Output voltage: ±15 V
  • Output current: ±100 mA max
  • Regulation: 0.05 % network & load

  • Ripple: 0.5 mV RMS max output

  • Connections: 9-pin DB-Socket connector

An example of connecting equipment for recording spectra

Example of connecting the SpectraLIA amplifier
The modulator (chopper) is installed on the input slot
The modulator (chopper) is installed on the input slot
Capacitor F#-matcher with filter wheel
Capacitor F#-matcher with filter wheel are connected to modulator
Connection diagram of equipment for recording spectra

Help & Support

Dear visitor, if you have any questions regarding the two-channel lock-in amplifier SpectraLIA, single-element detectors, or other electronics manufactured by SOL instruments, contact us!

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