The SCSI standard recommends proper resistor (Thevenin) termination at host and peripheral locations to eliminate transmission line effects. Dual Thevenin Termination Networks offer high integration and performance in a miniature QSOP or SOIC package, which saves critical board area and provides manufacturing cost and reliability efficiencies. A terminating resistror is used to reduce or eliminate unwanted reflections on a transmission line. It can perfom this function only when its resistance value matches the characteristic impedance of the transmission line. The resistors used for terminating the transmission lines should be noiseless, stable and functional at high frequencies.
High speed logic such as HSTL (High Speed Trans-ceiver Logic) require suitable signal termination. The SWRDT Dual Thevenin termination network provides 16 terminating channels per package, and optimizes signal integrity by reducing reflections and ringing. The terminations are available in a range of standard values and are ideal for use in HSTL busses. As seen in the device schematic, R1 is typically tied to V+ and serves as a pull-up resistor, while R2 functions as a pull-down resistor and is tied to ground (or the most negative supply voltage). In addition, the equivalent Thevenin resistance (R1 in parallel with R2) should match the impedance of the trace.Ground-bounce and crosstalk are virtually eliminated using four direct ground connections to the die substrate, as well as four double-bonded connections to V+, for a total of 8 commons. In addition, the resistors have an absolute tolerance of 1% which provides tight impedance-matching and results in greatly reduced reflections. This design provides optimal signal integrity..