Advance Information
MT88E45
1.00
0.95
0.90
0.85
0.80
0.75
0.70
Gain ratio for
Bellcore GS1, GS2
ETSI GS2 op amps
0.794
Gain ratio for ETSI
GS1 op amp
0.668
0.65
0.60
0.55
0.531
0.50
3.0
3.5
4.0
Nominal Vdd (Volts)
4.5
5.0
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.
13
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
