CY7C955-NC Cypress Semiconductor Corp, CY7C955-NC Datasheet - Page 73

• Manufacturer Part Number: CY7C955-NC
• Manufacturer: Cypress Semiconductor Corp

Specifications of CY7C955-NC

• Lead Free Status / RoHS Status: Not Compliant

Interface Termination and Biasing Schemes
PECL Input Termination and Biasing Recommendations
Figures 15 19 show how to connect different output types to
the CY7C955 PECL inputs. Differential termination and bias-
ing (Figure 15) is required for RXD, and is highly recommend-
ed for RRCLK, and TRCLK. Nevertheless it is also possible for
the input to accept single-ended signals. If the positive end of
a PECL input pair is tied to GND (with or without a pull-down
resistor), the negative input will become a single-ended input.
This input is self-biased to its threshold at V
because the negative input is used, the signal entering the chip
through the input are inverted.
Figure 15 shows a differential PECL connection. Whenever
possible, this differential PECL connection scheme should be
used. Differential signals are less susceptible to com-
mon-mode noise.
+ve–
PECL
Output
–ve –
PECL
Output
Figure 15. Differential PECL Termination (High Performance)
PRELIMINARY
CC
/2. Notice that
130
130
73
80
80
Figure 16 shows another possible type of a differential PECL
connection. Although this connection is allowed, the method
suggested in Figure 15 will give better switching characteris-
tics.
Figure 17 shows a CMOS connection; no termination is need-
ed if the trace is kept short. If the trace is long, follow common
transmission line termination practices.
Figure 18 shows a TTL connection. The 0.01 F AC-coupling
capacitor allows the CY7C955 inputs to self-bias itself to
V
input because the signal is close to static.
Figure 19 shows how to connect a single-ended PECL con-
nection to the ALOS input. ALOS is almost a static signal, so
the connection must be DC-coupled. A 330 resistor to GND
is needed, as a current sink is needed for the PECL output to
operate correctly.
CC
V
Vcc
/2. This connection scheme is not suitable for the ALOS
CC
RRCLK+ / RXD+
RRCLK– / RXD–
TRCLK+ /
TRCLK– /
CY7C955
CY7C955