MRI Receiver Protection PIN Diodes
Overview
DescriptionThere are two principal applications for which the MML4400 series are intended.
The first is MRI receiver protection from high-RF energy fields, including long RF pulses and RF spike pulses present in most MRI machines. The MML4400 series acts as a passive protector (limiter) for the MRI receiver’s low-noise amplifier (LNA). The diode assembly exhibits extremely low insertion loss, both in the on state (high power present) and the off state (receiver power present), so that the receiver’s noise figure is not increased by the protector circuit.
The second principal application is passive switching of surface-coil detuning and blocking circuits. In this case, the flow of the loop current during transmitter pulses turns on the diodes, without the use of a switch driver.
The MML4400 series can be combined with a PIN diode (UM7201SM), and the combination can be used to implement a semi-active detune or block circuit design. The MML4400 series devices turn on the PIN diode (used for higher-power switching) during the sinc(x) sidelobes, before the main pulse of the transmitter waveform (sinc(x) = [sin (x)]/x) occurs.
This surface mount limiter meets RoHS requirements according to EU directives 2011/65/EC and 2002/95 EC.
Key Features
- Designed for MRI applications
- Anti-parallel (unconnected pairs) option available with GM3 package
- Low capacitance at 0 V bias: 1.5 pF maximum
- Low conductance at 0 V bias: 40 μs maximum at F = 64 MHz
- Low magnetic construction surface mount package
- Passivated chip
- Compatible with automatic insertion equipment
- RoHS compliant and 260 °C reflow compatible
Applications/Benefits
- MRI Passive Receiver Protection
- MRI Passive Blocking Circuits
- MRI Passive Detuning Circuits
- MRI Passive Disable Circuits
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