SA58643 Datasheet, PDF (9/16 Pages) NXP Semiconductors – Excellent overload capability

NXP Semiconductors
SA58643
Single-Pole Double-Throw (SPDT) switch
The SA58643DP evaluation demo board (see Figure 19b. SA58643 board layout)
provides a stable RF layout. The demo circuit (see Figure 19a. Evaluation board
schematic) is constructed on 2-layer, 1-ounce copper, FR4 PCB material. The overall
thickness is 0.062 inches and has a dielectric constant, ε_r of 4.6. The transmission lines
are modeled for coplanar waveguide with both top and bottom ground. The 50 Ω
transmission line width is 1.388 mm, the gap from transmission line to top ground plane is
0.254 mm, and the dielectric thickness is 1.499 mm. To facilitate grounding, and support
low inductance ground returns, the top and bottom grounds are connected by
through-hole vias that are equal in diameter to the thickness of the PCB.
The top view in Figure 19b shows the placement of the circuit components. The RF input
(pin 4) is connected via a 50 Ω transmission line to a SMA connector. Symmetrical 50 Ω
transmission lines connect OUT1 and OUT2 (pins 5 and 8) to SMA connectors at
Outputs 1 and 2. A 50 Ω through-transmission line is provided as a calibration standard.
The outputs are selected via the DC logic level on ENCH1 (pin 2). Logic 1 level enables
Output1 (that is, connects it to the common RF input); Logic 0 enables Output2. The
positive supply, V_DD (pin 1) and AC_GND (pin 7) are decoupled using 100 nF,
0805 ceramic chip capacitors to ground.
13.2 Application examples
The SA58643 is a very versatile part and can be used in many applications. Figure 20
shows a block diagram of a typical digital RF transceiver front-end. In this application the
SA58643 replaces the duplexer which is typically very bulky and lossy. Due to the low
power consumption of the device, it is ideally suited for handheld applications such as in
CT2 cordless telephones. The SA58643 can also be used to generate Amplitude Shift
Keying (ASK) or On-Off Keying (OOK), and Frequency Shift Keying (FSK) signals for
digital RF communications systems. Block diagrams for these applications are shown in
Figure 21 and Figure 22, respectively.
For applications that require a higher isolation at 1 GHz than obtained from a single
SA58643, several SA58643s can be cascaded as shown in Figure 23. The cascaded
configuration will have a higher loss, but greater than 35 dB of isolation at 1 GHz and
greater than 65 dB at 500 MHz can be obtained from this configuration. The isolation and
matching of the two channels over frequency is shown in Figure 9 and Figure 10,
respectively. By modifying the enable control, an RF multiplexer/demultiplexer or antenna
selector can be constructed. The simplicity of the SA58643 coupled with its ease of use
and high performance lends itself to many innovative applications.
The SA58643 switch terminates the OFF channel in 50 Ω. The 50 Ω resistor is internal
and is in series with the external AC bypass capacitor. Matching to impedances other than
50 Ω can be achieved by adding a resistor in series with the AC bypass capacitor (that is,
25 Ω additional to match to a 75 Ω environment).
SA58643_1
Product data sheet
Rev. 01 — 20 November 2006
© NXP B.V. 2006. All rights reserved.
9 of 16