SSM2135

Rev. G | Page 12 of 16

Single Supply Differential Line Driver

Signal distribution and routing is often required in audio systems,

particularly portable digital audio equipment for professional

applications. Figure 35 shows a single-supply line driver circuit

that has differential output. The bottom amplifier provides a

2 V dc bias for the differential amplifier to maximize the output

swing range. The amplifier can output a maximum of 0.8 V rms

signal with a 5 V supply. It is capable of driving into 600 Ω line

termination at a reduced output amplitude.

5V

1/2

SSM2135

1/2

SSM2135

AUDIO IN

100µF

1kΩ

DIFFERENTIAL

AUDIO OUT

5V

1/2

SSM2135

1kΩ

2.5kΩ

100Ω

5V

7.5kΩ

5kΩ

1µF

0.1µF

2V

10kΩ

1kΩ

10µF + 0.1µF

Figure 35. Single-Supply Differential Line Driver

Single-Supply Differential Line Receiver

Receiving a differential signal with minimum distortion is

achieved using the circuit in Figure 36. Unlike a difference

amplifier (a subtractor), the circuit has a true balanced input

impedance regardless of input drive levels; that is, each input

always presents a 20 kΩ impedance to the source. For best

common-mode rejection performance, all resistors around the

differential amplifier must be very well matched. Best results

can be achieved using a 10 kΩ precision resistor network.

1/2

SSM2135

AUDIO

OUT

1/2

SSM2135

20kΩ

5V

5V

1/2

SSM2135

DIFFERENTIAL

AUDIO IN

100Ω

5kΩ

1µF

0.1µF

2.5kΩ

5V

7.5kΩ

10Ω

10µF

20kΩ

20kΩ

2V

20kΩ

20kΩ

10µF + 0.1µF

Figure 36. Single-Supply Balanced Differential Line Receiver

Pseudoreference Voltage Generator

For single-supply circuits, a reference voltage source is often

required for biasing purposes or signal offsetting purposes. The

circuit in Figure 37 provides a supply splitter function with low

output impedance. The 1 μF output capacitor serves as a charge

reservoir to handle a sudden surge in demand by the load as

well as providing a low ac impedance to it. The 0.1 μF feedback

capacitor compensates the amplifier in the presence of a heavy

capacitive load, maintaining stability.

The output can source or sink up to 12 mA of current with a

5 V supply, limited only by the 100 Ω output resistor. Reducing

the resistance increases the output current capability. Alternatively,

increasing the supply voltage to 12 V also improves the output

drive to more than 25 mA.

1/2

SSM2135

V+ = 5V TO 12V

R3

2.5kΩ

R4

100kΩ

R2

5kΩ

R1

5kΩ

C1

0.1µF

V+

2

OUTPUT

C2

1µF

Figure 37. Pseudoreference Generator