TEKTRONIX 5A22N
High-Gain Differential Amplifier Plug-In
Functional Characteristics
The Tektronix 5A22N is a sophisticated differential amplifier module engineered for the Tektronix 5000-series oscilloscope system. Its primary function is to measure the voltage difference between two points where neither point is at ground potential. This capability is vital in avoiding ground loops and for measuring signals superimposed on much larger common-mode voltages. The 5A22N stands out for its extreme sensitivity, allowing users to probe down to microvolt levels with significant accuracy.
Unlike standard vertical amplifiers, the 5A22N offers comprehensive control over the frequency response of the amplified signal. This is achieved through independent controls for upper and lower frequency limits, essentially serving as an integrated bandpass filter. By narrowing the bandwidth to match the signal of interest, users can effectively eliminate high-frequency thermal noise or low-frequency hum (such as 50/60 Hz interference), resulting in a clear, measurable waveform on the oscilloscope screen.
Technical Specifications
Derived from original Tektronix documentation, the following specifications highlight the precision of the 5A22N module:
Feature SpecificationDeflection Factor (Sensitivity) 10 μV/div to 5 V/div in a 1-2-5 sequence
Bandwidth (-3 dB) DC to 1 MHz (at most sensitivity settings)
Common-Mode Rejection Ratio (CMRR) 100,000:1 from DC to 100 kHz (at 10 μV/div)
Input Impedance 1 MΩ paralleled by approx. 47 pF
Max Common-Mode Voltage ±10 V (at 10 μV/div to 10 mV/div)
High Frequency Limit (Selectable) 100 Hz to 1 MHz in decade steps
Low Frequency Limit (Selectable) DC, 0.1 Hz to 10 kHz in decade steps
Input Coupling AC, DC, or GND (Independent for both inputs)
Advanced Differential Performance
Exceptional Common-Mode Rejection
The hallmark of the 5A22N is its Common-Mode Rejection Ratio (CMRR). In many electronic environments, signals are plagued by noise that is present on both signal lines—this is common-mode noise. The 5A22N utilizes a highly balanced input stage to subtract this common noise, amplifying only the difference between the two inputs. With a ratio of 100,000:1, the module can suppress up to 100 volts of common-mode signal to reveal a 1-millivolt differential signal, providing unparalleled clarity in complex electrical environments.
Selectable Bandwidth Control
To optimize the signal-to-noise ratio, the 5A22N includes dual-filter controls. The "Upper 3 dB Point" and "Lower 3 dB Point" knobs allow the user to create a customized frequency window. For example, when measuring biological signals (like an EKG) that occupy low frequencies, the user can set the upper limit to 100 Hz and the lower limit to 0.1 Hz. This filtering drastically reduces the "fuzz" on the trace caused by laboratory radio frequency (RF) interference or high-frequency digital switching noise.
Applications in Research and Industry
The Tektronix 5A22N is a staple in diverse fields due to its high sensitivity and differential capability:
Biomedical Engineering: Measuring physiological signals such as EEG, EKG, and nerve impulses where signals are in the microvolt range and susceptible to 60 Hz hum.
Power Supply Design: Measuring ripple and noise on power rails without causing ground shorts or being affected by large DC offsets.
Physical Sciences: Monitoring outputs from low-level transducers, thermocouples, and strain gauges in experimental setups.
Audio Engineering: Analyzing balanced audio lines and crosstalk in high-fidelity circuitry.
System Compatibility and Integration
The 5A22N is designed for the Tektronix 5100 and 5400 series oscilloscope mainframes. It occupies one vertical plug-in slot. In a four-bay mainframe, multiple 5A22N modules can be used to compare different differential signals simultaneously. The module is strictly "N" (Non-readout), meaning the scale factors are read directly from the front panel knobs rather than displayed on the CRT of readout-capable mainframes.
Installation and Maintenance
When installing the 5A22N, ensure the mainframe power is off. Slide the module into the vertical compartment until the latch clicks. For the most accurate microvolt measurements, it is recommended to allow the module to warm up for at least 20 minutes to reach thermal stability. Periodically, the DC Balance should be checked by setting the inputs to GND and adjusting the front-panel pot so that the trace does not jump when switching sensitivity ranges.
Conclusion
The TEKTRONIX 5A22N remains one of the most respected differential amplifiers in the history of test and measurement. Its combination of microvolt sensitivity, selectable frequency filtering, and robust CMRR makes it an essential tool for any application where low-level signals must be extracted from noisy backgrounds. For users of the 5000-series oscilloscope platform, the 5A22N provides the precision and reliability necessary for the most demanding scientific and engineering challenges.
