M521 MA-COM | Alldatasheet

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Positive Voltage Control of GaAs MMIC Control Devices Rev. V3 Application Note M521 Visit www.macomtech.com for additional data sheets and product information. M/A-COM Technology Solutions Inc. and its affiliates reserve the right to make changes to the product(s) or information contained herein without notice. SW-239 with +5 V Supply Figure 2b. Positive Voltage Control Configuration of the SW-239

Applications

This type of voltage floating technique can be used in most control component applications. A typical switch and digital attenuator application are pre- sented in Figure 2. Each application is similar in that the source of the FET’s are biased at +5 V and the gates can be controlled by 0 and +5 V. In all cases, the ground pins which have a source connection must be AC coupled with the shortest possible path to ground. The AT-210 is shown as an example of a digital attenuator which is floated. Pins 10 through 15 are normally grounded, but in this case are floated to the +5 V supply and AC coupled to ground. One of the RF connections must also be tied to +5 V to ensure the source of the se ries FET’s are floated. As mentioned above, all efforts to minimize induc- tance to ground must be taken to ensure the full attenuation range of the devic e. A truth table for the digital attenuator in the floated configuration is shown in Table 1. Attn (dB) VC4 VC4 VC3 VC3 VC2 VC2 VC1 VC1 0 1 0 1 0 1 0 1 Ref. 1 0 0 1 0 1 0 1 1 0 1 1 0 0 1 0 1 2 1 0 1 0 0 1 0 1 3 0 1 0 1 1 0 0 1 4 1 0 0 1 1 0 0 1 5 0 1 1 0 1 0 0 1 6 1 0 1 0 1 0 0 1 7 0 1 0 1 0 1 1 0 8 1 0 0 1 0 1 1 0 9 0 1 1 0 0 1 1 0 10 1 0 1 0 0 1 1 0 11 0 1 0 1 1 0 1 0 12 1 0 0 1 1 0 1 0 13 0 1 1 0 1 0 1 0 14 1 0 1 0 1 0 1 0 15 Control Inputs Table 1. AT-210 Truth Table (+5 V Control) The SW-239 is shown as an example of a SPDT switch which is floated using this technique. Pins 2, 7, and 8 are normally ground and must be floated with +5 V as well as being AC coupled to ground. A +5 V supply is also required at the RF common to ensure that the source of the series FET’s are floated. The resistors R1 and R3 will result in slower switchi ng speed, but will minimize coupling of RF signals along the +5 V line. A truth table for this device in the floated configuration is given in Table 2. Control A Control B RF1 RF2

0 V +5 V ON OFF

+5 V 0 V OFF ON Table 2. SW-239 Truth Table

Positive Voltage Control of GaAs MMIC Control Devices Rev. V3 Application Note M521 Visit www.macomtech.com for additional data sheets and product information. M/A-COM Technology Solutions Inc. and its affiliates reserve the right to make changes to the product(s) or information contained herein without notice. The AT-250 is a VVA that can, similarly, be floated for positive bias operation as shown in Figure 3. AT-250 8765 4321 Values: C1-C4: 1000pF R1-R2: 10 kΩ A RF1 +5V RF2 C4 R2 +5V Figure 3. Positive Voltage Control Configuration of the AT-250