Monolithic ICs have been the trend for millimeter wave circuits. However, improvements in assembly technologies and the fabrication of passive circuits make hybrid IC approaches using discrete devices more feasible at millimeter wave frequencies. The hybrid approach is quite flexible and less expensive than monolithic integration, with performance largely determined by the packaged devices that are used.

Figure 1

Figure 1 Top (a) and bottom (b) view of the YSD040SLPP01.

YOKOWO has developed a low cost packaged Schottky barrier diode for millimeter wave applications. The YSD040SLPP01 operates from X- into Ka-Band. With a junction capacitance as low as 30 fF typical at Vc = 0 V, the diode is suitable for detector, switch and mixer applications. The diode package is made of a laminated polymer film with an internal cavity that effectively suppresses the extrinsic capacitance (see Figure 1). The flat, surface-mount package, 1.6 × 1.2 mm, can easily be attached to a circuit board by solder reflow. In addition to the cathode and anode pads, the device provides two ground pads forming a ground-signal-ground (GSG) transmission line to provide a better signal feed at the I/O pads. No package resonance is observed up to 40 GHz. This packaging approach offers several advantages over bare die: ease of handling, storage, assembly – including high volume production, repair and durability in a chemical environment.

Figure 2

Figure 2 24 GHz SPST switch layout.

Figure 3

Figure 3 SPST switch performance.

 

Figure 4

Figure 4 24 GHz single balanced mixer layout.

A SPST switch for the 24 GHz ISM-Band was developed to demonstrate the performance of the YSD040SLPP01. The circuit design uses a single diode in shunt with a series transmission-line reflector (see Figure 2).The length of the line L is designed so that the reactance of the series connection of the positively-biased diode and the line is zero at 24 GHz. The circuit board is a commercially available material with er = 3.5 and tan d= 0.002. The performance of the SPST switch is shown in Figure 3. The control voltage is 0 V for off and +3 V for on. At 24.5 GHz, the insertion loss is 1.5 dB, and the isolation 23 dB. An on/off ratio of over 20 dB is achieved.

 

Another application demonstrating the diode is a 24 GHz mixer. The circuit design (see Figure 4) is a simple single balanced mixer using a rat-race power combiner/divider. The bias for the diodes is applied in series. The circuit board material is the same as used for the SPST switch, and the diodes are attached to the board by solder reflow. Conversion loss vs. LO power is shown in Figure 5. Less than 7 dB is measured with LO power of 0 to 3 dBm across an IF range of 1 to 100 MHz. The sensitivity of the mixer (see Figure 6) is -80 dB or better, which is excellent and sufficient for radar/sensor applications.

These simple hybrid circuits using one or two packaged diodes show excellent performance, confirming that the YSD040SLPP01 Schottky diode is suitable for detector, switching and mixer applications up to Ka-Band. In addition to the YSD040SLPP01, YOKOWO provides bare die diodes with performance in Ka-, U-, V-, E- and W-Band (the YSD080SLBD01 and YSD110SLBD01).

Figure 5

Figure 5 Single balanced mixer conversion loss.

Figure 6

Figure 6 Single balanced mixer sensitivity.

YOKOWO Co. Ltd.
Tokyo, Japan
www.yokowo.co.jp/english/product/semiconductor.shtml