EUA2011

DS2011 Ver 1.1 Dec. 2007

13

Summing Two Differential Input Signals

Two extra resistors are needed for summing differential

signals (a total of 5 components). The gain for each input

source can be set independently (see equations (4) and (5),

and Figure 33).

-----------------------(4)

-----------------------(5)

If summing left and right inputs with a gain of 1 V/V, use

If summing a ring tone and a phone signal, set the

ring-tone gain to Gain 2 = 2 V/V, and the phone gain to

Gain 1 = 0.1 V/V. The resistor values would be. . .

Figure 33. Application Schematic with EUA2011

Summing Two Differential Inputs

Summing a Differential Input Signal and a

Single-Ended Input Signal

Figure 34 shows how to sum a differential input signal

and a single-ended input signal. Ground noise can couple

in through IN+ with this method. It is better to use

differential inputs. The corner frequency of the

assure that each input is balanced, the single-ended input

must be driven by a low-impedance source even if the

input is not in use

------------------------ (6)

-----------------------(7)

-----------------------------------------(8)

If summing a ring tone and a phone signal, the phone

signal should use a differential input signal while the ring

tone might be limited to a single-ended signal. Phone gain

is set at gain 1 = 0.1 V/V, and the ring-tone gain is set to

gain 2 = 2 V/V, the resistor values would be…

The high pass corner frequency of the single-ended input

is set by CI2. If the desired corner frequency is less than

20 Hz...

Figure 34. Application Schematic with EUA2011

Summing Input and Single-Ended Input Signals

1

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