Overview
The model 7280 DSP Lock-in Amplifier is an exceptionally versatile instrument with outstanding performance. With direct digital demodulation over an operating frequency extending up to 2.0 MHz, output filter time constants down to 1 µs and a main ADC sampling rate of 7.5 MHz it is ideal for recovering fast changing signals. But unlike some other high frequency lock-ins, it also works in the traditional audio frequency band.
In addition to its excellent technical specifications, it is also very easy to use. The front panel is dominated by a large electro-luminescent display panel, used both to show the instrument's outputs and for adjusting its controls via a series of menus. Controls are set by a combination of the use of the keys surrounding the display and the keypad, while four cursor-movement keys simplify use of the graphic display menus.
Users of the SIGNAL RECOVERY (formerly PerkinElmer/EG&G) 7260 and 7265 will find switching to the 7280 very easy, since we've designed it with a similar menu structure. The only significant changes are in some of the control menus, where the better resolution of the display allows both the controls and the instrument outputs to be shown simultaneously, for even faster feedback on the effects of control adjustments.
Naturally, the instrument includes the extended operating modes like dual reference, dual harmonic and virtual reference made popular by the 7260 and 7265, as well as the spectral display mode used to aid reference frequency selection. It also includes GPIB and RS232 interfaces for remote computer control and a range of auxiliary analog and digital inputs and outputs. Software support is available in the form of a LabVIEW driver supporting all instrument functions, and the Acquire™ data acquisition software. The driver and a demonstration version of the software, DemoAcquire, are available for download from this site.
In summary, if you need a lock-in capable of working beyond the traditional audio frequency band but still want the drift-free performance that only digital demodulation brings, then look no further – you have found it in the SIGNAL RECOVERY Model 7280.
- 0.5 Hz to 2 MHz operation
- Direct digital demodulation without down conversion
- 7.5 MHz main ADC sampling Rate
- 1 µs to 100 ks output time Constants
- Dual Reference, Dual Harmonic and Virtual Reference modes
- Spectral display mode
- Scanned probe microscopy
- Optical measurements
- Audio studies
- AC impedance studies
- Atomic force micorscopy
The model 7280 DSP lock-in amplifier is an exceptionally versatile instrument with outstanding performance.
Specifications
| Signal Channel | |
| Voltage Input | |
| Modes | A only, -B only or Differential (A-B) |
| Full-scale Sensitivity | |
| 0.5 Hz ≤ F ≤ 250 kHz | 10 nV to 1 V in a 1-2-5 sequence |
| 250 kHz < F ≤ 2.0 MHz | 100 nV to 1 V in a 1-2-5 sequence |
| Max. Dynamic Reserve | > 100 dB |
| Impedance | 100 MΩ // 25 pF |
| Maximum Safe Input | 20 V pk-pk |
| Voltage Noise | 5 nV/√Hz @ 1 kHz |
| C.M.R.R. | > 100 dB @ 1 kHz |
| Frequency Response | 0.5 Hz to 2.0 MHz |
| Gain Accuracy | ±0.3% typ, ±0.6% max. (full bandwidth) |
| Distortion | -90 dB THD (60 dB AC gain, 1 kHz) |
| Line Filter | attenuates 50, 60, 100, 120 Hz |
| Grounding | BNC shields can be grounded or floated via 1 kΩ to ground |
| Current Input | |
| Mode | Low Noise, Normal or Wide Bandwidth |
| Full-scale Sensitivity | |
| Low Noise | 10 fA to 10 nA in a 1-2-5 sequence |
| Normal | 10 fA to 1 µA in a 1-2-5 sequence |
| Wide Bandwidth | |
| F ≤ 250 kHz | 1 pA to 100 µA in a 1-2-5 sequence |
| F > 250 kHz | 10 pA to 100 µA in a 1-2-5 sequence |
| Max. Dynamic Reserve | > 100 dB |
| Frequency Response (-3 dB): | |
| Low Noise | ≥ 500 Hz |
| Normal | ≥ 50 kHz |
| Wide Bandwidth | ≥ 1 MHz |
| Impedance | |
| Low Noise | < 2.5 kΩ @ 100 Hz |
| Normal | < 250 Ω @ 1 kHz |
| Wide Bandwidth | < 25 Ω @ 10 kHz |
| Noise | |
| Low Noise | 13 fA/√Hz @ 500 Hz |
| Normal | 130 fA/√Hz @ 1 kHz |
| Wide Bandwidth | 1.3 pA/√Hz @ 1 kHz |
| Gain Accuracy | ± 0.6% typ, midband |
| Line Filter | attenuates 50, 60, 100, 120 Hz |
| Grounding | BNC shield can be grounded or floated via 1 kΩ to ground |
| Reference Channel | |
| TTL Input | |
| Frequency Range | 0.5 Hz to 2.0 MHz |
| Analog Input | |
| Impedance | 1 MΩ // 30 pF |
| Sinusoidal Input Level | 1.0 V rms* |
| Frequency Range | 0.5 Hz to 2.0 MHz |
| Squarewave Input Level | 250 mV rms |
| Frequency Range | 2 Hz to 2 MHz |
| *Note: Lower levels can be used with the analog input at the expense of increased phase errors | |
| 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 acquisition |
| External Reference | 2 cycles + 50 ms |
| Reference Frequency Meter Resolution | 1 ppm or 1 mHz, whichever is the greater |
| Demodulator and Output Processing | |
| Output Filters | |
| X, Y and R outputs only | |
| Time Constant | 1 µs to 1 ms in a 1-2-5 sequence, and 4 ms |
| Slope (roll-off) | 6 and 12 dB/octave |
| All outputs | |
| Time Constant | 500 µs to 100 ks in a 1-2-5 sequence |
| Slope | 6, 12, 18 and 24 dB/octave |
| Synchronous Filter | Available for F < 20 Hz |
| Offset | Auto and Manual on X and/or Y: ±300% full-scale |
| Absolute Phase Measurement Accuracy | ≤ 0.01° |
| Oscillator | |
| Frequency | |
| Range | 0.5 Hz to 2.0 MHz |
| Setting Resolution | 1 mHz |
| Absolute Accuracy | ± 50 ppm |
| Distortion (THD) | -80 dB @ 1 kHz and 100 mV rms |
| Amplitude (rms) | |
| Range | 1 mV to 1 V |
| Setting Resolution | 1 mV |
| Accuracy | ±0.2% |
| Stability | 50 ppm/°C |
| Output Impedance | 50 Ω |
| Sweep | |
| Amplitude Sweep | |
| Output Range | 0.000 to 1.000 V rms |
| Law | Linear |
| Step Rate | 20 Hz maximum (50 ms/step) |
| Frequency Sweep | |
| Output Range | 0.5 Hz to 2.0 MHz |
| Law | Linear or Logarithmic |
| Step Rate | 1 kHz maximum (1 ms/step) @ output time constant settings of 500 µs or longer; 140 ms/point otherwise |
| Outputs | |
| Main Analog (CH1 and CH2) Outputs: | |
| Function | X, Y, R, Θ, Noise, Ratio, Log Ratio and User Equations 1 & 2. |
| Amplitude | ±2.5 V full-scale; linear to ±300% full-scale |
| Impedance | 1 kΩ |
| Update Rate | |
| X, Y or R @ TC £ 4 ms | 7.5 MHz |
| All outputs @ TC ³ 500 µs | 1 kHz |
| Reference Output | |
| Waveform | 0 to 3 V rectangular wave, active in External Reference Mode only |
| Impedance | TTL-compatible |
| Power – Low Voltage | ±15 V at 100 mA rear panel 5-pin 180° DIN connector for powering SIGNAL RECOVERY preamplifiers |
| General | |
| Power Requirements | |
| Voltage | 110/120/220/240 VAC |
| Frequency | 50/60 Hz |
| Power | 200 VA max |
| Dimensions | |
| Width | 17¼" (435 mm) |
| Depth | 19" (485 mm) |
| Height | |
| With feet | 6" (150 mm) |
| Without feet | 5¼" (130mm) |
| Weight | 25.4 lb (11.5 kg) |
