SN55107A, SN75107A, SN75107B, SN75108A

DUAL LINE RECEIVERS

SLLS069D – JANUARY 1977 – REVISED APRIL 1998

12

POST OFFICE BOX 655303

APPLICATION INFORMATION

SN75108A dot-AND output connections

The SN75108A line receiver features an open-collector-output circuit that can be connected in the dot-AND

logic configuration with other similar open-collector outputs. This allows a level of logic to be implemented

without additional logic delay.

Output

SN75108A

SN75108A

SN5401/SN7401 or

Equivalent

Dot-AND

Connection

Figure 14. Dot-AND Connection

increasing common-mode input voltage range of receiver

The common-mode voltage range (CMVR) is defined as the range of voltage applied simultaneously to both

input terminals that, if exceeded, does not allow normal operation of the receiver.

The recommended operating CMVR is

±3 V, making it useful in all but the noisiest environments. In extremely

noisy environments, common-mode voltage can easily reach

±10 V to ±15 V if some precautions are not taken

to reduce ground and power supply noise, as well as crosstalk problems. When the receiver must operate in

such conditions, input attenuators should be used to decrease the system common-mode noise to a tolerable

level at the receiver inputs. Differential noise is also reduced by the same ratio. These attenuators were omitted

intentionally from the receiver input terminals so the designer can select resistors that are compatible with his

particular application or environment. Furthermore, the use of attenuators adversely affects the input sensitivity,

the propagation delay time, the power dissipation, and in some cases (depending on the selected resistor

values) the input impedance; thereby reducing the versatility of the receiver.

The ability of the receiver to operate with approximately

±15 V common-mode voltage at the inputs has been

checked using the circuit shown in Figure 15. Resistors R1 and R2 provide a voltage-divider network. Dividers

with three different values presenting a 5-to-1 attenuation were used to operate the differential inputs at

approximately

±3 V common-mode voltage. Careful matching of the two attenuators is needed to balance the

overdrive at the input stage. The resistors used are shown in Table 1.

Table 1

Attenuator 1:

R1 = 2 k

Ω,

R2 = 0.5 k

Ω

Attenuator 2:

R1 = 6 k

Ω,

R2 = 1.5 k

Ω

Attenuator 3:

R1 = 12 k

Ω,

R2 = 3 k

Ω