The Keithley 428-PROG Programmable Current Amplifier is a precision instrument engineered to amplify low-level current signals with sub-picoamp noise performance and high dynamic range. A feedback current circuit topology delivers fast rise times and exceptional signal-to-noise ratio, surpassing traditional electrometers and picoammeters. Programmable gain, selectable filtering, and integrated bias voltage supply enable flexible operation across research, quality control, and automated test environments. IEEE-488 interface provides remote control and system integration.
## Technical Specifications
**Current Amplification**
• Nine gain ranges: 10³ V/A to 10¹¹ V/A (with ×10 gain enabled); 10³ V/A to 10¹⁰ V/A standard
• Decade increment selection
• ×10 gain selection degrades accuracy by 0.2% and temperature coefficient by 0.003%/°C
**Response and Filtering**
• Selectable rise times: 2 µs to 300 ms
• Minimum rise time of 2 µs at 10³ V/A and 10⁴ V/A gain ranges (10⁵ V/A with ×10 enabled)
• Second-order Bessel-function low-pass filter; defeatable for 6 dB/octave roll-off applications
• Programmable filter rise time: 10 µs to 300 ms
**Noise Performance**
• RMS noise: 1.2 fA rms
**Input Characteristics**
• Voltage burden: <200 µV (18–28°C) for inputs <100 µA; <10 mV for inputs ≥100 µA
• Temperature coefficient: 20 µV/°C
• Maximum overload: 100 V (10⁴ to 10¹¹ V/A ranges); 10 V (10³ V/A range); higher voltages must be current-limited at 10 mA
**Programmable Bias Supply**
• Range: ±5 V
• Resolution: 2.5 mV
• Accuracy: ±(1.1% of reading + 25 mV)
**Current Suppression**
• Up to ±5 mA
## Key Features
• ZERO CHECK and OFFSET functions maintain gain accuracy
• Programmable ±5 V bias voltage supply eliminates external bias requirements
• Background current suppression to ±5 mA
• Selectable rise times decouple speed from noise performance across nine ranges
## Typical Applications
• Low-level photodiode and photomultiplier current measurement
• Scanning tunneling electron microscope control loops
• Dark current characterization
• Leakage current monitoring in semiconductor testing
## Compatibility & Integration
• IEEE-488 (GPIB) interface for remote programming and automated test system integration
