The AD8116* is a wideband 256-point analog switch with 16 high-impedance inputs and 16 buffered outputs. With this "non-blocking" type of crosspoint switch, any input signal can be routed to one or more (including all) of the outputs, as programmed via an 80-bit serial word (Figure 1).
Figure 1. Non-blocking crosspoint switching.
The individual output buffer amplifiers can drive 150-W video loads with 0.01% differential gain and 0.01° differential phase errors, and with flat response (to within 0.1 dB) to 60 MHz (200 MHz for -3 dB). Each output has an independent Disable feature to permit cascading of multiple AD8116s to build larger switch arrays. This complete 256-point solution is offered in a tiny 128-lead TQFP (5/8" x 5/8") and consumes only 90 mA of supply current. It can be used alone or in groups, with daisy-chained serial data, to expand the numbers of paths to over 200 inputs and/or outputs. Figure 2 shows the scheme of input and output connections for a 48 x 48 array architecture, using 9 AD8116s. In addition, the serial control data is daisy-chained from DATA OUTs to DATA INs.
Figure 2. 48 x 48 crosspoint (2,304-point) array.
Video crosspoint switches are used primarily for routing high-speed signals, including composite video (NTSC, PAL, SECAM, etc.), component video (YUV, RGB, etc.), in applications such as studios, video-on-demand, in-flight entertainment, and surveillance and video-teleconferencing.
Figure 3 is a functional block diagram of the AD8116. Note the inputs, switch matrix, set of output buffers, individually controlled 3-state enable/disable switches, and the DATA IN and DATA OUT pins. The 80 bits of switching data are coded in 16 5-bit groups, associated with each of the outputs, starting with OUT15. The first bit indicates whether the output is enabled or disabled, and the last four indicate the input to which it is connected. After the shift register is filled with the 80 bits of new control data, the data is transferred to the parallel switch control latches, where it resides until updated or the power is turned off.
The switch channels can be used individually to switch high-density single-ended composite video signals or paired to handle differential signals. So a single AD8116 can form an 8 x 8 differential crosspoint switch. For RGB or YUV data, three channels can be used for each video channel. Crosstalk is less than -70 dB, with -105 dB of isolation, at 5 MHz.
The output buffers, when disabled, are at high impedance. This permits outputs of multiple AD8116s to be paralleled with minimal loading of the on channel. In expanded configurations, (for example the 48 x 48 array of Figure 2), the inputs associated with a given range of outputs are paralleled and the outputs are wire-OR'd together. Of course, arrays need not be square (for example 128 x 16).
The AD8116JST is specified for ±5-V power supplies and for operation at temperatures from 0 to 70°C. It dissipates 900 mW (3.5 mW per switch point). Housing is in a 14 mm x 14 mm 128- lead plastic TQFP. A 4-layer evaluation board (AD8116EB) is available to demonstrate the device's performance; the board is available as a fully populated design-in kit, with BNC-type connectors, plus custom cable, Windows-based software for control via a PC printer port, and board layout files. Price of the AD8116JST is $90 in 1000s, and the AD8116-EB design-in kit is priced at $395.