FIT1045A
Wideband Injection Transformer
Description
The FIT1045A is a small-signal injection transformer that has been optimized for control loop stability testing over a wide frequency range. This transformer provides isolation between expensive benchtop test instrumentation (such as a VNA or a Frequency Response Analyzer) and a device under test (DUT), to enable closed-loop response measurements while introducing minimal parasitic loading to preserve measurement fidelity.
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This transformer offers a wide usable bandwidth, low parasitic capacitance, high common-mode voltage withstanding capability, and is densely packaged in a rugged powder-coated (scratch resistant) enclosure.
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While occupying less than half the bench space of products with similar bandwidths, the FIT1045A offers best-in-class saturating current limits, which means it can be driven harder without loss of signal fidelity.
Detailed Specifications
Connectorization
Injection transformers are typically constructed with a BNC input interface and either a BNC or Banana Jack output (DUT-facing) interface. The FIT1045A is equipped with a BNC output as this allows users to maintain a clean connection from injector to DUT -- e.g., by way of BNC-to-mini grabber leads. Both input and output connectors are impedance controlled to 50 Ohms over the product's rated bandwidth.
Parasitics and Saturation
The FIT1045A is carefully hand-wound and every core is parametrically tested prior to assembly for quality assurance. The nominal isolation capacitance (input-to-output) of the FIT1045A transformer is 85 pF at 3MHz, which helps to keep DUT loading to a minimum for improved measurement fidelity. Despite occupying a smaller overall mechanical package, the FIT1045A contains a relatively large core for its size, allowing for reduced turn count and therefore reduced winding resistance, while boasting higher core saturation margin for the same bandwidth. See FIT1045A datasheet for detailed specifications.
Bandwidth
All injection transformers have a load-dependent bandwidth. And therefore, bandwidth must be specified against a known source and load impedance. The S21 gain plotted below represents a typical response from the FIT1045A when driven by a 50 Ohm source impedance and terminated into a 5 Ohm load [Figure 1]. The 5 Ohm termination is chosen here to represent a typical low-value injection resistor as one might find in a power supply control loop.
Figure 1: 5 Ohm Load
When the load termination is raised, the passband will raise with it, as it forms a divider against the source impedance, and both the upper and lower (-3dB) cutoff frequencies will move to the right [Figure 2]. For a detailed application note explaining the consequence of passband flatness on stability testing, please see the App Notes section.
Figure 2: High Impedance Load
Fusing
Blue Dot Laboratories has destructively tested the FIT1045A so you don't have to. Each unit contains a secondary-side fast-blow fuse that will interrupt a high-current fault condition. Note: no fusing curve can guarantee protection under all fault scenarios. Please observe absolute maximum operating conditions as specified in the FIT1045A datasheet to avoid damage. This fuse is not designed to be customer-serviceable. If you think you've fused your FIT1045A, please reach out via the contact form to request service (opening your FIT1045A will void its manufacturing warranty).
Mechanicals
At Blue Dot, we've spent our share of capital on laboratory equipment and we're often disappointed to find expensive tools packaged in flimsy plastic enclosures. The FIT1045A mechanicals are overdesigned, on purpose. Rather than using injection molded plastics, the FIT1045A is housed in a black anodized enclosure (2) with powder coated endcaps (4) that clamp against a gasket (3) to prevent dust and moisture intrusion. The added mass and rubberized feet (1) keep the injector firmly planted on your lab bench.
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Note: opening your FIT1045A voids the manufacturing warranty. If you believe your unit to be out of spec or faulted, contact us via the form above for a swift reply.
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Where to Buy?
The FIT1045A is currently offered by the following distributors:
