Model 7270 - Overview

The model 7270 sets a new standard for general-purpose DSP lock-in amplifiers.  We've taken advantage of the developments in technology since the first DSP lock-in amplifiers were introduced in the early 1990’s to update the core design, but made sure that we’ve included all the best features of our model 7265 and 7280 instruments. What’s more, the new architecture has allowed us to offer even better specifications in an instrument that is physically much more compact than older designs. The result is a lock-in amplifier of outstanding performance that is easy to use and suitable for all measurements over a frequency range extending from 1 mHz to 250 kHz.

Versatility
In common with other models in our range, the 7270 offers much more than just dual phase lock-in detection at the reference frequency of an applied signal. We’ve included features unique to SIGNAL RECOVERY instruments such as dual reference and dual harmonic detection, which allow signals at two different frequencies to be measured simultaneously. The spectral display mode shows the power spectral density of the input signal, making it easy to avoid interfering signals when selecting a reference frequency. It is now even possible to perform tandem demodulation. In this mode an amplitude-modulated signal at a (high) “carrier” frequency is first demodulated at that frequency. The resulting in-phase output, at short time constant settings, is a signal at the modulating frequency which is then passed forward for detection by a second set of demodulators running at the same modulating frequency. Such detection techniques, which can be used in pump-probe measurements, have until now required two separate instruments with an analog connection between them.

Fast Data Processing
The main ADC sampling rate and the rate at which the analog signal outputs are updated is 1 MSa/s, giving excellent performance when used at short output filter time constant settings, such as in scanned probe measurements. But we’ve also increased the maximum rate at which data can be stored to the internal curve buffer to 1 μs per point, allowing for the first time direct capture of instrument outputs when using these short time constants. The buffer length has also been increased to 100,000 sets of points, giving recording times of 100 ms at the fastest sampling rates. What’s more, in the fast capture mode the length does not need to be divided by the number of outputs being stored, making it possible, for example, to store the full 100,000 points of X, Y and auxiliary ADC1 values at the same time.

Remote Control
The built-in RS232, USB and Ethernet connections allow full operation from a controlling computer. We offer a comprehensive software package, Acquire, that can operate the instrument via any of these interfaces and makes it easy to set up and run complex experiments, such as frequency response measurements, as well as allowing remote control of every instrument function. Users who wish to do their own programming can use our ActiveX control and toolkit (SRInstComms), or free LabVIEW driver, to simplify the task.

See what you’ve been missing...
In summary, if you’re looking for a general purpose lock-in to work in the range 1 mHz to 250 kHz then you need look no further - you’ve found it in the SIGNAL RECOVERY model 7270.

• 1 mHz to 250 kHz operating frequency range
• 1.0 MHz main ADC sampling rate
• 10 µs to 100 ks output filter time constants
• Dual Reference, Dual Harmonic and Virtual Reference operating Modes
• Internal data buffer for recording instrument outputs at rates down to 1 µs per point
• USB, RS232, and Ethernet computer interfaces

The model 7270 sets a new standard for general-purpose DSP lock-in amplifiers. Model 7270 Specifications

Signal Channel
Voltage Input
Modes	A only, -B only or Differential (A-B)
Freq. Response	1 mHz < F < 250 kHz
Full-scale Sensitivity	2 nV to 1 V in a 1-2-5 sequence (e.g. 2 nV, 5 nV, 10 nV, 20 nV, etc.)
Z - FET	10 MΩ // 25 pF, AC or DC coupled
Z - Bipolar	10 kΩ // 25 pF, input must be DC coupled
Max safe input	±12.0 V
Vin Noise - FET	5 nV/√Hz @ 1 kHz
Vin Noise - Bipolar	2 nV/√Hz @ 1 kHz
C.M.R.R.	> 100 dB @ 1 kHz degrading by > 6 dB/octave with increasing frequency
Gain Accuracy	±0.5% typ, ±1.0% max
Distortion	-90 dB THD (60 dB AC gain, 1 kHz)
Current Input
Mode	Low Noise (10E8 V/A) or Wide Bandwidth (10E6 V/A)
Full-scale Sensitivity
Low Noise	2 fA to 10 nA in a 1-2-5 sequence
Wide Bandwidth	2 fA to 1 µA in a 1-2-5 sequence
Frequency Response (-3 dB):
Low Noise	1 mHz < F < 500 Hz minimum
Wide Bandwidth	1 mHz < F < 50 kHz minimum
Impedance
Low Noise	< 2.5 kΩ @ 100 Hz
Wide Bandwidth	< 250 Ω @ 1 kHz
Noise
Low Noise	13 fA/√Hz @ 500 Hz
Wide Bandwidth	130 fA/√Hz @ 1 kHz
Gain Accuracy	±2.0% typ, midband
Max. Dynamic Reserve	> 100 dB
Grounding	BNC shield can be grounded or floated via 1 kΩ to ground
Signal Monitor Amplitude	±1 V FS
Output Impedance	1 kΩ
Reference Channel
Reference Input
Frequency Range	1 mHz to 250 kHz
Analog Input (front panel)
Impedance	1 MΩ // 30 pF
Sinusoidal Input Level	1.0 V rms*
Frequency Range	0.5 Hz to 250 kHz
Squarewave Input Level	250 mV rms
Frequency Range	2 Hz to 250 kHz
Reference Channel
Phase Set Resolution	0.001° increments
Phase Noise at 100 ms TC, 12 dB/octave slope:
Internal Reference	< 0.0001° rms
External Reference	< 0.01° rms @ 1 kHz
Orthogonality	90° ± 0.0001°
Acquisition Time
Internal Reference	instantaneous
External Reference	2 cycles + 1 s
Demodulator and Output Processing
Harmonic Rejection	-90 dB
Output Filters
Time Constant	10 µs to 100 ks in a 1-2-5 sequence
Slope (roll-off):
TC < 5 ms	6 or 12 dB/octave
TC > 5 ms	6, 12, 18 or 24 dB/octave
Synchronous Filter	Available for F < 20 Hz
Offset	Auto and Manual on X and/or Y: ±300% full-scale
Phase Measurement Resolution	< 0.01º
Oscillator - General
Freq. Range	1 mHz to 250 kHz
Setting Resolution	1 mHz
Absolute Accuracy	± 50 ppm
Amplitude Range	1 µV to 5 V
Max. Setting Resolution	1 µV
Output Impedance	50 Ω
Sweep
Frequency Sweep
Output Range	1 mHz to 250 kHz
Law	Linear or Logarithmic
Step Rate	1 kHz maximum (1 ms/step)
Amplitude Sweep
Output Range	0.000 to 1.000 V rms
Law	Linear
Step Rate	20 Hz maximum (50 ms/step)
Oscillator Output
Amplitude
Accuracy	±0.2% typ
Stability	50 ppm/ºC
Distortion (THD)	-80 dB @ 1 kHz and 100 mV rms
Data Storage Buffer
Size	100,000 data points
Max. Storage Rate
Fast Mode	up to 1 MHz (X1, Y1, X2, Y2, ADC1, Demod I/P 1, Demod I/P 2)
Normal Mode	1 kHz
User Settings
	Up to 8 complete instrument settings can be saved or recalled at will from non-volatile memory
Interfaces
	USB 2.0, Ethernet, and RS232 allow complete control of instrument settings, and data readout.
General
Power Requirements
Voltage	110/120/220/240 VAC
Frequency	50/60 Hz
Power	40 VA max
Dimensions
Width	15½" (390 mm)
Depth	7¼" (185 mm)
Height
With feet	7¼" (185 mm)
Without feet	6½" (170 mm)
Weight	12.8 lb (5.8 kg)
	Specifications subject to change without notice

Model 7270

Overview
The model 181 is a current-to-voltage preamplifier of low noise and low input impedance designed to amplify the extremely low currents encountered in such areas as photometry and semiconductor research. In photometric applications the low input noise allows the use of photodetectors with dark currents as low as 10-14 A/√Hz, while the wide frequency range permits high modulation frequencies to avoid 1/f noise and power-line pick-up.

The unit has a high dynamic range, allowing small AC currents to be amplified without overload in the presence of quiescent (DC) detector currents up to ten times the current to voltage converter setting. In semiconductor applications its low input impedance permits the actual bias voltage applied to the device under test to be measured without having to correct for the effects of back bias.

Six switch-selectable sensitivity settings from 10-4 A/V to 10-9 A/V are available and the instrument has a usable frequency range from DC to 200 kHz. A signal monitor connector is provided on the rear panel and there is an overload indicator light on the front panel.

Bias Control
A bias control (accessible through an opening in the bottom of the unit) allows the application of a detector bias voltage at the input connector in the range 0 V to -5 V, with a nominal source impedance of 10-5/S, where S is the selected sensitivity. For example, if the sensitivity is set to 10-7 A/V then the source impedance will be 10-5/10-7, or 100 Ω. In some cases it
may prove convenient to use this bias control to cancel the effect of DC bias accompanying the input signal.

DC Zero Control
A second control, also accessible through an opening in the bottom of the unit, allows the internal electronics to be DC zeroed.

Power
The unit can be powered from an external low voltage, a lock-in amplifier via a suitable power cable, or the models PS0055 or PS0056 remote line power supply modules.

• Low input impedance
• Low noise
• Single-ended virtual ground input
• Adjustable sensitivity
• DC to 200 kHz frequency response
• Detector bias control
• Photodiode amplification
• Photomultiplier amplification
• Ion collector amplification
• Electron multiplier amplification

Specifications
General
DC coupled current to voltage amplifier with adjustable sensitivity and a maximum frequency response extending from DC to 200 kHz. Adjustable negative detectors bias.  Single-ended virtual ground input and single-ended AC coupled output via BNC connectors.

Powered from external DC power supplies.

DC coupled current to voltage amplifier with adjustable sensitivity and a maximum frequency response extending from DC to 200 kHz. Adjustable negative detectors bias.  Single-ended virtual ground input and single-ended AC coupled output via BNC connectors.Powered from external DC power supplies.

Input
Sensitivity	10-4 A/V to 109 A/V in six angles
Overload Indicator	Indicates that instantaneous (DC plus peak AC) current has exceeded amplifier capability - see table below
Frequency Response	see table and Figure 1
Input Impedance	See Figure 2
Noise Current	See Figure 3
Outputs
Monitor Output	600Ω rear-panel BNC connector permits monitoring of the input signal
Main Output      Level	6.5 V rms maximum
Impedance	1Ω k nominal
Output Attenuator	Provides optional 1:10 attenuation of output voltage
Power	±15 V or ±24 V at 30 mA
General
Dimensions (excluding connectors)	4.5" wide x 6.6" deep x 2.7" high (114 mm wide x 168 mm deep x 69 mm high)
Weight	1.2lbs. (500 g)

Model 181

Overview
The model 181 is a current-to-voltage preamplifier of low noise and low input impedance designed to amplify the extremely low currents encountered in such areas as photometry and semiconductor research. In photometric applications the low input noise allows the use of photodetectors with dark currents as low as 10-14 A/√Hz, while the wide frequency range permits high modulation frequencies to avoid 1/f noise and power-line pick-up.

The unit has a high dynamic range, allowing small AC currents to be amplified without overload in the presence of quiescent (DC) detector currents up to ten times the current to voltage converter setting. In semiconductor applications its low input impedance permits the actual bias voltage applied to the device under test to be measured without having to correct for the effects of back bias.

Six switch-selectable sensitivity settings from 10-4 A/V to 10-9 A/V are available and the instrument has a usable frequency range from DC to 200 kHz. A signal monitor connector is provided on the rear panel and there is an overload indicator light on the front panel.

Bias Control
A bias control (accessible through an opening in the bottom of the unit) allows the application of a detector bias voltage at the input connector in the range 0 V to -5 V, with a nominal source impedance of 10-5/S, where S is the selected sensitivity. For example, if the sensitivity is set to 10-7 A/V then the source impedance will be 10-5/10-7, or 100 Ω. In some cases it
may prove convenient to use this bias control to cancel the effect of DC bias accompanying the input signal.

DC Zero Control
A second control, also accessible through an opening in the bottom of the unit, allows the internal electronics to be DC zeroed.

Power
The unit can be powered from an external low voltage, a lock-in amplifier via a suitable power cable, or the models PS0055 or PS0056 remote line power supply modules.

• Low input impedance
• Low noise
• Single-ended virtual ground input
• Adjustable sensitivity
• DC to 200 kHz frequency response
• Detector bias control
• Photodiode amplification
• Photomultiplier amplification
• Ion collector amplification
• Electron multiplier amplification

Specifications
General
DC coupled current to voltage amplifier with adjustable sensitivity and a maximum frequency response extending from DC to 200 kHz. Adjustable negative detectors bias.  Single-ended virtual ground input and single-ended AC coupled output via BNC connectors.

Powered from external DC power supplies.

DC coupled current to voltage amplifier with adjustable sensitivity and a maximum frequency response extending from DC to 200 kHz. Adjustable negative detectors bias.  Single-ended virtual ground input and single-ended AC coupled output via BNC connectors.Powered from external DC power supplies.

Input
Sensitivity	10-4 A/V to 109 A/V in six angles
Overload Indicator	Indicates that instantaneous (DC plus peak AC) current has exceeded amplifier capability - see table below
Frequency Response	see table and Figure 1
Input Impedance	See Figure 2
Noise Current	See Figure 3
Outputs
Monitor Output	600Ω rear-panel BNC connector permits monitoring of the input signal
Main Output      Level	6.5 V rms maximum
Impedance	1Ω k nominal
Output Attenuator	Provides optional 1:10 attenuation of output voltage
Power	±15 V or ±24 V at 30 mA
General
Dimensions (excluding connectors)	4.5" wide x 6.6" deep x 2.7" high (114 mm wide x 168 mm deep x 69 mm high)
Weight	1.2lbs. (500 g)

Model 181