LI5600-Serie - Lock-in Verstärker

Lock-in amplifiers that measure extremely small alternating signals hidden deep within noise are used in a wide range of advanced research fields, including scanning probe microscopes, terahertz spectroscopy and spintronics.
NF's newest lock-in amplifier LI5600 series is 2-phase, 2-frequency digital lock-in amplifier that delivers a high level of stability with post-phase detection digital signal processing. The series covers all areas of key functionality required for increasing reliability when measuring very small signals, such as an outstanding dynamic reserve up to 100 dB, update rates up to approximately 1.5 M samples/s (LI5660/LI5655), and smooth, high-speed 16-bit amplitude resolution output response.
The LI5660 series is equipped with the latest functions such as simultaneous 2-frequency measurements (except for LI5645) and subharmonic measurements to meet the needs for advance measurements in a wide range of applications and fields.

  • Max. Measurement Frequency: 11 MHz
  • Fractional Harmonic Measurement
  • Dual Frequency Simultaneous Measurement
  • External 10 MHz Synchronous Input


High-response and High-stability

  • Time Constant
    The minimum time constant is 1 μs for LI5660/LI5655 (5 μs for LI5650/LI5645).
    Our newest lock-in amplifiers have achieved high-frequency and high speed response.
    screen: time constant
  • Synchronous Filter
    This is an integer-period moving-average filter. Ripple caused by detection is greatly reduced, and the output is nearly settled in the averaging interval (integer period), so the time constant can be reduced (to obtain faster response)
  • High-speed Locking Even at Low Frequencies
    It takes just about two cycles to lock on to the reference signal even at low frequencies. Furthermore, a moving average filter synchronized with the signal cycle obtains a high-speed response with a small ripple.
  • Outstanding Dynamic Reserve
    Phase detection and subsequent processing are performed digitally. Output zero drift at high gains is smaller than the analog system, and up to 100 dB dynamic reserve can be obtained (measurement can be performed with a noise 100,000 times larger than the sensitivity, namely the signal full scale).

Up to 11 MHz with the wide-band, high-frequency input terminal (LI5660)

Voltage measurements can be made with a single end (A) or differential (A-B) input, as well as 10 Vrms input (C) and high-frequency input (HF) terminals with the LI5660. The HF input terminals can be used to measure up to 11 MHz.

Fractional Harmonic Measurements

screen: fractional harmonicMeasurements can be made at submultiple frequencies of the fundamental wave (1 to 63) / (1 to 63).
Provide measurement of fractional times frequency of the fundamental wave. In 2-frequnecy measurement mode of LI5660/LI5655/LI5645, each primary PSD and secondary PSD individual frequency setting available. For example, primary PSD set as n/m times with reference signal frequency, and secondary PSD set as n times with reference signal frequency or set as different frequency from primary frequency.
Harmonic measurements are made at integral multiples between two measurement frequencies (f2 = (f1 x n) ). In this case, distortion in thef1 side signal results in an integral multiple frequency (harmonic), which cannot be distinguished from the f2 signal. With subharmonic measurements, measurements can be conducted with the f2 = f1 x n/m relationship, which means that even if distorted harmonics are generated with f1, the frequency can be set so that it does not affect f2. f2 harmonic measurements are possible without being affected by f1 harmonics.

Dual-frequency Simultaneous Measurements

screen: Detection Mode (Dual 1)LI5660/LI5655/LI5650 come with 2-phase sensitive detectors (PSD), allowing simultaneous measurement of two frequency components that are included in a single input signal. Measurements that previously required two lock-in amplifiers using the dual beam method can now be made with a single lock-in amplifier.
Ratio calculations can be made by determining the ratio between the measured value and reference value, and the secondary PSD can be connected in cascade to the primary PSD, to run detection using the secondary PSD after detecting the signal with the primary PSD.

Detection Mode Primary PSD Secondary PSD Function
SINGLE* Fundamental / Fractional Harmonic None 2-phase detection is at one frequency.
DUAL1 Fundamental / Fractional Harmonic Fundamental / Harmonic Simultaneous measurement of the fundamental wave and its harmonic components included in a single input signal
DUAL2 Primary Frequency Secondary Frequency Simultaneous measurement of two individual harmonic components included in a single input signal
CASCADE Primary Frequency Secondary Frequency The secondary PSD is connected in cascade to the primary PSD.

*The detection mode of LI5645 is "SINGLE" mode only.


External 10 MHz Synchronization

screen: External 10 MHz Reference InputSynchronizing operation of other devices such as a signal generator and the LI5600 series using a 10 MHz frequency source allows synchronization to any frequency (can be configured) without having to use an external reference signal (REF IN).




Wide Range of Functions in a Thin, Compact Body

  • LI5660
    LI5660 front
    LI5660 back


LI5660 LI5655 LI5650 LI5645
Frequency Range 0.5 Hz to 11 MHz 0.5 Hz to
3 MHz
1 mHz to
250 kHz
1 mHz to
250 kHz
Signal Input Voltage (A, A-B)
10 Vrms input (C)
HF input (HF)
Current (I)
Sensitivity Voltage Input A, A-B:
10 nV to 1 V F.S.
(0.5 Hz to 3 MHz)
C: 1 mV to 10 V F.S.
(0.5 Hz to 3 MHz)
2 mV to 1 V F.S..
(10 kHz to 11 MHz)
10 nV to 1 V F.S.
Current Input 10 fA to 1 µA F.S.
Input Referred Noise Voltage 4.5 nV/√Hz
(supplement value)
PSD 2-phase,
Dynamic Reserve 100 dB 100 dB 100 dB 100 dB
Time Constant 1 µs to 50 ks 5 µs to 50 ks
Analog Output Max. Update Rate Approx.
1.5 M samples/s
780 k samples/s
Fractional Harmonic Measurement
Dual Frequency Simultaneous Measurements
External 10 MHz Synchronous Input
Measurement Parameter X, Y, R, θ, DC, NOISE
Remote Control Interface USB, GPIB, RS-232, LAN


SPM (Scanning Probe Microscope) Signal Processing


Scanning probe microscopes such as STM (scanning tunnel microscope) and AFM (atomic force microscope) use a nanoscale probe at the tip to scan the surface of a sample. The signal between the probe and the sample is detected to observe the electronic state and structure of the sample surface, as well as its physical and chemical properties. Lock-in amplifiers are used to control the distance between the sample and probe. The LI5600 series can also be used with high resonance frequency cantilever movement in the MHz range, and setting a smaller time constant (from 1 μs) allows high-speed scanning to generate images in a shorter time. The synchronization filter can drastically reduce phase detection output ripples, resulting in much higher quality images, generated at a faster speed. Lock-in amplifiers are also used for signal processing such as modulation signal demodulation with KFM (surface potential microscope) as well as STM and ATM.

Light Transmission Measurements (Suppression of Illuminant Fluctuation)


Using both the dual-frequency simultaneous and fractional harmonic measurement functions allows fluctuation corrections of light sources and other sources using the dual beam method (ratio measurement) with a single LI5660/ LI5655/LI5650. Applying negative feedback to the reference cell signal also stabilizes the strength of the light source. The integral multiple (n x), integral inverse (1/m x) and fraction (n/m x) of the reference signal frequency can be configured, allowing it to be used easily with light chopper frequency ratios. When integral ratios are used, signals cannot be distinguished from harmonic components generated by distortion in the signal, however there is no impact on the harmonics if fraction ratios are used. The 10 MHz synchronization function can also be used to synchronize operation with external signal generators, allowing detection of any two frequencies.

Hall Coefficient Measurement (Difference Frequency Measurement)


The hall voltage is proportional to the product of two signals (current and magnetic field), and its frequency is the difference frequency (and sum) of the two signals. Synchronizing an external signal source, which generates a current and magnetic field, with the LI5600 series at an external 10 MHz allows measurement of the difference frequency signal of any two frequencies without having to arrange an external reference signal (difference frequency). (when used with a signal generator with a 2-channel output and frequency reference output) If the original frequency is a integral* ratio, the fractional harmonic measurement function can also be used to measure the difference frequency signal. Either method avoids crosstalk interference from the external reference signal.

Other applications

  • Spectroscopy (material science using Auger electron spectroscopy, photoacoustic spectroscopy, Raman spectroscopy, etc.)
  • Measurement of optical properties (intensity, absorption, scattering, transmission, etc.)
  • Optical application measurements (optical gyro, detection of distance, speed, vibration, etc.)
  • Magnetic measurements (evaluation of magnetic materials, vibration-type magnetometer, magnetic detection using SQUID)
  • Evaluation of various sensors (measurements of physical quantities detected by optical, magnetic, and piezoelectric elements, chemical changes, etc.)
  • Null detection with impedance bridge
  • Impedance measurements (minute impedance, minute capacity, chemical impedance)
  • Thermal diffusivity measurement of thin film materials