TDR IC and High Bandwidth Sample & Hold Amplifiers in Test Instrumentation
Precision test instrumentation demands ICs that can capture signals others simply cannot. Two of the most critical components in high-speed test equipment are the TDR IC and the high bandwidth sample and hold amplifier – and in modern instrumentation design, they are almost always found working together on the same chip.
What is a TDR IC?
A Time Domain Reflectometer IC is an integrated circuit that generates a fast voltage step stimulus and measures the reflected waveform to detect impedance discontinuities in transmission lines, cables, connectors, and PCB traces.
In a TDR IC, two functional blocks work together:
Step Stimulus Generator
A controlled-amplitude differential voltage step is injected into the device under test. The faster the rise time – typically 10 picoseconds or less – the finer the spatial resolution of the impedance measurement.
Sample and Hold Front End
The reflected waveform is captured by a high bandwidth sample and hold amplifier. The S&H samples the returning signal at precise intervals, digitizing the reflected waveform for analysis.
This is why TDR ICs and high bandwidth sample and hold circuits are inseparable – one generates the stimulus, the other captures the response.
What is a High Bandwidth Sample and Hold Amplifier?
A sample and hold amplifier captures an analog signal at a precise moment in time and holds that value steady for analog-to-digital conversion. In high-speed instrumentation, bandwidth is everything.
Why Bandwidth Matters
A sample and hold IC with insufficient bandwidth distorts the signal before it is even captured. For instruments measuring 28G NRZ, PAM4 signals, or sub-nanosecond TDR responses – you need analog bandwidths of 30 GHz, 45 GHz, or 60 GHz to capture what is actually there.
Low Noise is Non-Negotiable
In precision instrumentation, input-referred noise directly limits measurement accuracy. High performance S&H ICs achieve noise floors as low as 1mVrms – preserving signal fidelity across the full sampling rate range.
Key Applications
TDR ICs and high bandwidth sample and hold amplifiers are at the heart of:
Digital Sampling Oscilloscopes
Sub-sampled DSOs rely on high bandwidth S&H front ends to extend effective measurement bandwidth far beyond what real-time ADCs can achieve.
Time Domain Reflectometry Instruments
Board trace, connector, and cable impedance testing – from bench instruments to handheld TDR tools and automated test equipment.
High-Speed Communications ATE
Testing 100G and 400G optical and copper links requires S&H ICs capable of capturing PAM4 eye diagrams at symbol rates up to 60 GBaud.
RF and Microwave Test Equipment
Wideband sub-sampled receivers and signal analyzers use high bandwidth S&H ICs to extend measurement range while keeping power dissipation low.
Why FMAX for TDR ICs and High Bandwidth Sample & Hold
FMAX Technologies has spent 25+ years developing TDR ICs and high bandwidth sample and hold amplifiers for the most demanding test instrumentation applications.
Our product portfolio covers 30 GHz, 45 GHz, and 60 GHz bandwidths – all implemented in advanced SiGe BiCMOS for the noise performance and speed that precision instruments demand:
- FX362 — 30 GHz TDR IC with integrated Sample & Hold AFE, 10ps rise-time step stimulus
- FX372 — 60 GHz Sample & Hold IC for ultra-high-speed signal acquisition
- FX331 — 32 GHz differential S&H amplifier, 485mW, 1.6mVrms noise, QFN16
- FX332 — 32 GHz S&H amplifier, ultra-low 1mVrms noise, pin-compatible upgrade to FX331
Every IC ships with full datasheet and high-speed evaluation board support.
Explore FMAX TDR and Sample & Hold ICs →
FAQs
A TDR IC integrates both a step stimulus generator and a sample and hold front end on one chip - making it a complete analog front end for reflectometry instruments. A standalone S&H IC provides only the sampling function, used in oscilloscopes, ATE, and sub-sampled receivers where no stimulus is needed.
Your S&H bandwidth should be at least equal to the highest frequency component in your signal. For 28G NRZ signals, 30 GHz bandwidth is the minimum. For PAM4 at 60 GBaud or TDR with 10ps rise-time resolution, 60 GHz bandwidth is required.
FMAX uses advanced SiGe BiCMOS - specifically IBM/GF 8HP, 9HP, and IHP SG13G2 process nodes - chosen for their transistor fT performance at frequencies above 30 GHz where standard CMOS cannot compete.
Yes. Beyond commercial products, FMAX offers full mixed-signal ASIC development services for custom instrumentation chip design. Contact us to discuss your requirements.