Input and output buffers are needed to complete the system. Standard buffers are 16 channels and are available SMB connectors that can be converted to BNC connectors using patch panels. A complete 128×128 system requires eight input and eight output buffers. These buffers serve up to three different purposes:

• They transform impedances to allow the solid state switch fabric to be used for signals requiring other than two wire analog, for example 50 ohm coax.
• Input Buffers can be used to reduce signals to levels where they can be safely switched by the matrix.
• Output Buffers can have preset gains to boost signals to required voltages.
• A typical Output buffer is shown schematically in Fig. 2. Resistors Rs and Ri set the input impedance and also attenuate the input signal (if needed), while Rout determines the output impedance. The circuit is typically built with one of several standard small signal Op Amps, but custom amplifiers are also possible. Specifications for a typical small signal amplifier are shown below.

Specifications (signal with buffers)

• Characteristic Impedance: 50 or 75 Ohms
• Small Signal Bandpass (±1.0 V) 140 MHz (±1.5dB)
• Large Signal Bandpass (±4.0 V) 75 MHz (-3dB)
• Crosstalk: non adjacent path -75 dB @ 20 MHz
• Crosstalk: adjacent path -47 dB @ 10 MHz
• Input/ Output Isolation: -80 dB @ 10 MHz
• Switching Speed: 50 ns + Control Interface Delay