MT88E45AS datasheet(13/27 Pages) MITEL

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Advance Information

MT88E45

Figure 8 - Gain Ratio as a Function of Nominal Vdd

Gain Setting Resistor Calculation Example for Figure 8:

•

For the desired nominal Vdd, use Figure 8 to determine approximate Av.

•

For the GS1 op-amp, start with the 0dB gain setting resistor values of R50dB, R60dB and R70dB. In

Figure 7 these values are 53K7, 60K4 and 464K respectively. Keep C1,C2,R1,R2,R3,R4 as in Figure 7

to maintain the highpass corner frequency constant for all gain settings.

•

For the desired gain setting of Av:

R7Av= R70dB x AV

Scaled for desired gain. Choose

the closest standard resistor value as R7Av.

Actual Av from now on is R7Av/R70db

R5Av= R50dB x AV

Scaled for good common mode range. Choose

the closest standard resistor value as R5Av.

1/R6Av = 1/R5Av - 1/R7Av

Calculate R6Av so that R5Av=R6Av || R7Av. Choose

the closest standard resistor value as R6Av.

•

Repeat for R10, R11, R12 for the GS2 op-amp.

Example:

•

For a gain of -3.5dB, Av=10

-3.5/20 = 0.668

•R7-3.5dB= 464K x 0.668 = 309K9, the closest standard resistor value is 309K.

Av is now 309K/464K = 0.666

•R5-3.5dB= 53K6 x 0.666 = 35K7, the closest standard resistor value is 35K7.

Therefore R6-3.5dB is calculated to be 40K4, the closest standard resistor value is 40K2.

3.0

3.5

4.0

4.5

5.0

Nominal Vdd (Volts)

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

0.668

0.531

0.794

Gain ratio for

Bellcore GS1, GS2

ETSI GS2 op amps

Gain ratio for ETSI

GS1 op amp

MT88E45AS Datasheet(PDF) 13 Page - Mitel Networks Corporation

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