The TA123 Bessel-Thomson Reference Filter 1.25 Gb/s is a specialised measurement accessory for optical communication and Gigabit Ethernet signal analysis.
It is intended for 1.250 Gb/s GBE signals and forms part of Pico Technology’s Bessel-Thomson filter family, where each filter is matched to a specific serial data rate.
The TA123 is used in the electrical path after optical-to-electrical conversion. A typical measurement chain is:
Optical transmitter → O/E converter → TA123 Bessel-Thomson filter → Sampling oscilloscope
Pico states that placing the correct BT filter between the O/E converter output and oscilloscope input helps the displayed waveform represent what an equalised optical receiver would see.
Designed for 1.25 Gb/s Gigabit Ethernet
The TA123 is specifically matched to:
- 1.250 Gb/s serial data
- Gigabit Ethernet
- Optical transmission testing
- Optical eye-diagram analysis
- Telecom and networking signal characterisation
Pico identifies TA123 as the dedicated 1.250 Gb/s GBE model in its Bessel-Thomson reference filter range.
Reference Receiver Response
The TA123 is not simply a general-purpose low-pass filter.
Its purpose is to apply the appropriate Bessel-Thomson reference response to the electrical signal before measurement.
This helps engineers evaluate parameters such as:
- Eye opening
- Rise time
- Fall time
- Pulse shape
- Overshoot
- Undershoot
- Timing behaviour
- Signal symmetry
- Receiver-oriented waveform quality
Using the correct reference response is important because measuring the same signal with excessive oscilloscope bandwidth can produce a waveform that does not accurately represent the receiver response used by the communication system.
Optical Eye-Diagram Analysis
The TA123 is well suited to optical eye-diagram measurements at 1.25 Gb/s.
Eye-diagram analysis can be used to evaluate:
- Eye height
- Eye width
- Crossing behaviour
- Rise and fall transitions
- Timing variation
- Pulse symmetry
- Overshoot and ringing
- Overall signal quality
The filter helps condition the waveform before it reaches the oscilloscope so the result is more representative of a reference optical receiver.
Optical-to-Electrical Measurement Chain
The TA123 works on the electrical signal, not directly on the optical fibre.
The correct sequence is:
- Optical signal is generated or received.
- An O/E converter converts the optical waveform into an electrical signal.
- The TA123 applies the 1.25 Gb/s Bessel-Thomson response.
- The oscilloscope captures and analyses the filtered electrical waveform.
This distinction should be clear on the RevineTech page because the TA123 is not an optical filter, transceiver or O/E converter.
Compatible PicoScope Systems
Pico Technology currently lists the TA123 filter family for use with:
- PicoScope 9221A
- PicoScope 9231A
- PicoScope 9321
These instruments can use the appropriate Bessel-Thomson filter to display measurements corresponding to the required optical receiver response.
Gigabit Ethernet Testing
The TA123 is suitable for applications involving optical Gigabit Ethernet systems and related 1.25 Gb/s serial communication links.
Typical uses include:
- Gigabit Ethernet transmitter testing
- Optical transceiver validation
- Fibre communication testing
- Network equipment development
- Optical module characterisation
- Telecom interface validation
- Research and educational laboratories
- Production signal verification
Passive Measurement Accessory
The TA123 is a fixed reference filter used directly in the signal path.
It does not require:
- USB control
- Software configuration
- Network connection
- PicoSDK
- Electronic switching
- User-selectable filter settings
The correct response is selected by choosing the appropriate filter model for the required data rate.
Bessel-Thomson Filter Family
Pico currently lists the following models:
| Model |
Bit Rate |
Communication Standard |
| TA120 |
51.8 Mb/s |
OC1 / STM0 |
| TA121 |
155 Mb/s |
OC3 / STM1 |
| TA122 |
622 Mb/s |
OC12 / STM4 |
| TA123 |
1.250 Gb/s |
GBE |
| TA124 |
2.488 Gb/s |
OC48 / STM16 |
| TA124 |
2.500 Gb/s |
InfiniBand 2.5G |
Why Correct Filter Selection Matters
Each Pico BT filter is intended for a specific serial data rate.
Using the wrong filter can affect the apparent:
- Rise time
- Fall time
- Eye opening
- Pulse shape
- Overshoot
- Timing response
- High-frequency content
For 1.25 Gb/s Gigabit Ethernet measurements, TA123 is the correct Pico reference filter.
Applications
The TA123 is suitable for:
- 1.25 Gb/s optical signal testing
- Gigabit Ethernet signal characterisation
- Optical eye-diagram analysis
- Optical transceiver testing
- Fibre communication development
- Telecom equipment validation
- Network interface testing
- Optical module development
- Production optical testing
- Research and development
- Engineering education
- Communication laboratory training
