Datasheet

7–195
Bias Voltage
V
IN
V
REF
V
CC
Input Stage
V
OUT
Bias Voltage
V
CC
Output Stage
Figure 3. Typical GTL Input and Output Cells
BTL Family Input and Output Structure
The BTL input receiver is a differential amplifier with one side connected to an internal reference voltage. The threshold is
designed with a narrow window (V
IH
= 1.62 V and V
IL
= 1.47 V). Unlike GTL, BTL requires a separate supply voltage for the
threshold circuit to eliminate any noise generated by the switching outputs. The output driver is an open-collector output with
a termination resistor selected to match the bus impedance. When the device is turned off, the output is pulled up to the output
supply voltage (V
TT
= 2.1 V typical). The inputs and outputs work independently of the device’s V
CC
. They can communicate
with devices designed for 5-V or 3.3-V V
CC
. The TTL input is a 5-V CMOS inverter, and the output is a bipolar output similar
to the ABT output structure.
1
BTL requires three power supplies: the main power supply (V
CC
), the bias generator supply
(BG V
CC
), and the bias supply voltage (BIAS V
CC
) that establishes a voltage between 1.62 V and 2.1 V on the BTL outputs when
V
CC
is not connected. The maximum operating frequency of the BTL family is 75 MHz, depending on the application as well
as the board layout. Figure 4 shows a typical BTL input and output circuit.
V
OUT
V
CC
Input Stage
Output Stage
V
REF
V
IN
V
CC
Figure 4. Typical BTL Input and Output Cells