F2910 SPST Absorptive RF Switch with Constant Impedance Technology by IDT

Provides an overview of the IDT F2910, a broadband single-pole, single-throw (SPST) absorptive switch developed for a wide range of wireless and RF applications. With an operating frequency range of 30 to 8000 MHz, the F2910 is a high-linearity, low-insertion loss 50-ohm switch that delivers exceptional RF performance. The device is ideal for 4G/LTE-Advanced base stations, portable wireless applications, point-to-point, public safety infrastructure, and test equipment.

The F2910 features IDT’s industry-first Kz constant impedance technology, which maintains near-constant impedance when switching RF ports and improves hot switching ruggedness. The device offers excellent linearity and isolation performance while providing a 50-ohm termination on the output port when in isolation mode. The F2910 uses a single supply voltage and supports 3.3 V or 1.8 V control logic for ease of design.

Presented by Mark Schrepferman, product manager at IDT. For more information about IDT's RF switches, visit http://www.idt.com/products/rf-products/rf-switches.

TRANSCRIPT

Hello. My name is Mark Schrepferman. I'm a Product Manager at IDT's RF Business. Today I'd like to introduce the F2910 RF switch.
 
The F2910 single pole, single throw switch is the newest addition to our growing RF switch portfolio. The device has an operating frequency range of 30 to 8,000 MHz and has excellent RF performance. This device incorporates our new constant impedance feature which I'll talk about later.
 
Now let's take a closer look at some of the key performance attributes at 4GHz. An insertion loss of 0.67 dB; isolation, 41 dB; return loss, 20 dB; an IP3 of 65 dBm and an IP2 of 118 dBm; P1dB of 35 dBm.
 
The device supports a wide supply voltage range of 2.7 to 5.5 volts in either 1.8 or 3.3-volt control logic. It has an operating temperature range of -55 to 105°C. And is in a small 2x2mm DFN package.
 
Some of the applications supported are 4G and LTE advanced base stations, distributed antennae systems, or DAS, as well as other communication equipment, as well as test and measurement.
 
Now I'd like to talk about constant impedance technology or Kz for short. Kz controls the impedance during the RF switching process. The upper-left drawing shows a simplified box diagram consisting of a driver amplifier connected to the switch input and an amplifier and antenna connected to each of the switch output paths. You can see the switch has the RF input connected to the lower RF output path.
 
Now let's take a look at the drawing in the lower right which shows the RF path to the switch. The RF input is now connected to the upper RF output path. The standard, or non-Kz switch, does not control the impedance when switching RF ports. This can result in a large voltage wave standing ratio, or VSWR, transient, shown in red. This could stress both the upstream and downstream components connected to the switch. In addition to the VSWR transient stressing other components, it will also create a voltage stress on the switch itself, possibly damaging it or reducing its reliability. A Kz switch, highlighted in blue, maintains near constant impedance when switching between RF ports, minimizing the VSWR transient or stress on the switch itself.
 
To show how Kz works I'll use an example of a single pole, single throw absorptive switch with and without Kz, switching the RF common path to each of the RF output ports, RF1 and 2. For simplicity, I've shown a single stack switch FET in a series-shunt configuration.
 
Let's look at the top-left drawing, the non-Kz, or standard, switch. The switch shows the RF signal path between RF common and RF1 with the unused RF2 path terminated to ground. Now let's switch the RF path connecting RF common to RF2. The standard switches do not control the timing very well on individual gate control signals when switching RF ports.
 
The top-center drawing shows that it's possible for both RF1 and RF2 series FETs and the shunt FETs to all be off at the same time resulting in a large impedance change. With all the FETs off, RF common goes from seeing 50 ohms to high impedance, creating a large VSWR transient on RF common, reflecting the signal back to the source. This transient would create a high voltage stress on the switch itself as well as any components connected to RF common.
 
Now let's look at the Kz switch example on the bottom. Kz controls the sequencing of the individual gate control signals when switching RF ports such that the FETs are neither on or off all at same time. This results in maintaining a near constant impedance during the switching event. Because the impedance is controlled, there's no VSWR transient or stress on the switch itself.
 
IDT offers a simple to use evaluation board to help our customers perform lab measurements. The board consists of a pin header across the top with power, ground, and logic control. There's an RF through calibration port to make it easy to de-embed the trace loss. And, finally, there is an RF connector on each of the RF ports to measure the device's performance.