Digital Lock-in Amplifier

LI5660/LI5655/LI5650/LI5645

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.

	Frequency range LI5660: 0.5 Hz to 11 MHz* *When HF input terminal used LI5655: 0.5 Hz to 3 MHz LI5650/LI5645: 1 mHz to 250 kHz
	Voltage measurement LI5660: 10 nV to 10 V*F.S. *When C input terminal used LI5655/LI5650/LI5645: 10 nV to 1 V F.S.
	Current measurement 10 fA to 1 £gA F.S. (except for LI5645)
	Minimum time constant LI5660/LI5655: 1 £gs LI5650//LI5645: 5 £gs
	Dynamic reserve 100 dB or more
	Analog output update rate LI5660/LI5655: up to approximately 1.5 M samples/s LI 5650/LI5645: up to approximately 750 k samples/
	Dual Frequency Simultaneous measurement (LI5660/LI5655/LI5650) Two sets of dual phase sensitive detectors enable two frequency components included in a single input signal to be measured simultaneously.
	Fractional Harmonic measurement Measurements at submultiple frequencies of the fundamental wave (1 to 63) / (1 to 63)
	External 10 MHz synchronous input Can be synchronized with the reference frequency of other devices by using an external reference frequency.
	Measurement parameters: X, Y, R, £c, DC, Noise
	Interfaces: USB, GPIB, LAN
	Thin 2U size (88 mm)

High-response and High-stability

	Time Constant	Time Constant
	The minimum time constant is 1 £gs for LI5660/LI5655 (5 £gs for LI5650/LI5645). Our newest lock-in amplifiers have achieved high-frequency and high speed response.
	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

Measurements 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.	Fractional Harmonic
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

2-phase (Rcos£c, Rsin£c), 2 PSDs (Primary PSD, Secondary PSD)

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 (Dual 1)

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.

Display and Sampling of Output Data

 High Speed Sampling of Analog Data

The digital data of output is sampled at high speed and converted to an analog signal.

• LI5660/LI5655: up to approximately 1.5 M samples/s
• LI5660/LI5655: up to approximately 1.5 M samples/s

It is useful to detect peak signals when measuring by differential calculus such as Auger electron spectroscopy.

 Digital Data Buffer Function

If the number of data points is large in high-speed measurement, it may not be possible to transfer all data due to the communication speed of the interface.
NF's lock-in amplifier has a data buffer function that temporarily stores digital data. By temporary storing the measurement data in a buffer and transferring the data sequentially, a large amount of data can be transmitted without loss.

External 10 MHz Synchronization

Synchronizing 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).	External 10 MHz Reference Input

Wide Range of Functions in a Thin, Compact Body

	LI5660

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