SR570 Low Noise Current Preamplifier

SR570 Low Noise Current Preamplifier

5 fA/√Hz input noise

1 MHz maximum bandwidth

1 pA/V maximum gain

Adjustable bias voltage

Two configurable signal filters

Variable input offset current

Line or battery operation

RS-232 interface

SR570 specifications

The SR570 is a low-noise current preamplifier capable of current gains as large as 1 pA/V. High gain and bandwidth, low noise, and many convenient features make the SR570 ideal for a variety of photonic, low temperature and other measurements.

Gain

The SR570 has sensitivity settings from 1 pA/V to 1 mA/V that can be selected in a 1-2-5 sequence. A vernier gain adjustment is also provided that lets you select any sensitivity in between.

Front Panel

Rear Panel

Gain can be allocated to various stages of the amplifier to optimize the instruments performance. The low noise mode places gain in the front end of the amplifier for the best noise performance. The high bandwidth mode allocates gain to the later stages of the amplifier to improve the frequency response of the front end. In the low drift mode, the input amplifier is replaced with a very low input-current op amp, reducing the instrument’s DC drift by up to a factor 1000.

Block Diagram

Filters

The SR570 contains two first-order RC filters whose cutoff frequency and type can be configured from the front panel. Together, the filters can be configured as a 6 or 12 dB/oct rolloff low-pass or high-pass filter, or as a 6 dB/oct rolloff band-pass filter. Cutoff frequencies are adjustable from 0.03 Hz to 1 MHz in a 1-3-10 sequence. A filter reset button is included to shorten the overload recovery time of the instrument when long filter time constants are used.

Input Offset and DC Bias

An input offset-current adjustment is provided to suppress any undesired DC background currents. Offset currents can be specified from ±1 pA to ±1 mA in roughly 0.1 % increments. The SR570 also has an adjustable input DC bias voltage (±5 V) that allows you to directly sink current into a virtual null (analog ground) or a selected DC bias.

SR570 Current Noise vs. Frequency

Low Noise Mode

High Bandwidth Mode

Toggle and Blanking

Two rear-panel, opto-isolated TTL inputs provide additional control of the SR570. A blanking input lets you quickly turn off/on the instrument's gain which is useful in preventing front-end overloading. A toggle input inverts the sign of the gain in response to a TTL signal allowing you to perform synchronous detection with a chopped signal.

Battery Operation

Three rechargeable lead-acid batteries provide up to 15 hours of battery-powered operation. An internal battery charger automatically charges the batteries when the unit is connected to the line. The charger senses the battery state and adjusts the charging rate accordingly. Two rear-panel LEDs indicate the charge state of the batteries. When the batteries become discharged they are automatically disconnected from the amplifier circuit to avoid battery damage.

SR570 Bandwidth

Low Noise Mode

High Bandwidth Mode

No Digital Noise

The microprocessor that runs the SR570 is "asleep" except during the brief interval it takes to change the instrument's setup. This ensures that no digital noise will contaminate low-level analog signals.

RS-232 Interface

The RS-232 interface allows listen-only communication with the SR570 at 9600 baud. All functions of the instrument (except power on) can be set via the RS-232 interface. The RS-232 interface electronics are opto-isolated from the amplifier circuitry to provide maximum noise immunity.

*Related Products* SIM918 Precision Current Preamplifier SR510/530 Lock-In Amplifiers SR810/830 DSP Lock-In Amplifiers SR850 DSP Lock-In Amplifier SR785 Dynamic Signal Analyzer SR560 Low-Noise Voltage Preamplifier

SR570 Specifications


Input
Inputs	Virtual null or user-set bias (±5 V)
Input offset	±1 pA to ±1 mA adjustable DC offset current
Maximum input	±5 mA
Noise	See graphs
Sensitivity	1 pA/V to 1 mA/V in 1-2-5 sequence (vernier adj. in 0.5 % steps)
Frequency response	±0.5 dB to 1 MHz. Adjustable front-panel frequency response compensation for source capacitance.
Grounding	Amplifier ground is fully floating. Amplifier and chassis ground are available at rear panel. Input ground can float up to ±40 V.

Filters
Signal filters	2 configurable (low-pass or high-pass) 6 dB/oct rolloff filters. -3 dB points are settable in a 1-3-10 sequence from 0.03 Hz to 1 MHz.
Gain allocation:
Low noise	Gain is allocated to the front end for best noise performance.
High bandwidth	Front-end gain is reduced for optimum frequency response.
Low drift	Low bias current amplifier is used for reduced drift at high sensitivity.
Filter reset	Long time constant filters may be reset with front-panel button.

Output
Gain accuracy	±(0.5 % of output + 10 mV) @ 25°C
DC drift	see table below
Maximum output	±5 V into a high impedance load

General
External blanking	TTL input sets gain to zero
External toggle	TTL input inverts gain polarity
Rear panel biasing	±12 VDC @ 200 mA, referenced to amplifier ground
Computer interface	RS-232, 9600 baud, receive only
Power	100/120/220/240 VAC, 6 watts charged, 30 watts while charging. Internal batteries provide 15 hours of operation between charges. Batteries are charged while connected to the line.
Dimensions	8.3" × 3.5" × 13.0" (WHL)
Weight	15 lbs. (batteries installed)
Warranty	One year parts and labor on defects in materials and workmanship

Sensitivity (A/V)		Bandwidth (-3 dB)*		Noise/?Hz**	Temp. coefficient ±(%input + offset)/°C	DC Input Impedance
	High BW	Low Noise	High BW	Low Noise	Low Drift (11 to 28 °C)	All Modes
10^-3	1.0 MHz	1.0 MHz	150 pA	150 pA	0.01 % + 20 nA	1 Ω
10^-4	1.0 MHz	500 kHz	100 pA	60 pA	0.01 % + 2 nA	1 Ω
10^-5	800 kHz	200 kHz	60 pA	2 pA	0.01 % + 200 pA	100 Ω
10^-6	200 kHz	20 kHz	2 pA	600 fA	0.01 % + 20 pA	100 Ω
10^-7	20 kHz	2 kHz	600 fA	100 fA	0.01 % + 2 pA	10 kΩ
10^-8	2 kHz	200 Hz	100 fA	60 fA	0.01 % + 400 fA	10 kΩ
10^-9	200 Hz	15 Hz	60 fA	10 fA	0.025 % + 40 fA	1 MΩ
10^-10	100 Hz	10 Hz	10 fA	5 fA	0.025 % + 20 fA	1 MΩ
10^-11	20 Hz	10 Hz	10 fA	5 fA	0.040 % + 20 fA	1 MΩ
10^-12	10 Hz	10 Hz	5 fA	5 fA	0.040 % + 20 fA	1 MΩ

* Frequency Compensation adjusted for flat frequency response
** Average noise in the frequency range below the 3 dB point but above the frequency where 1/f noise is significant

Lambda Photometrics

The leading supplier of cutting edge technology