Advance Information MT88E46
1.000
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
PRELIMINARY
0.63095
3.0
3.5
4.0
4.5
5.0
Nominal Vdd (Volts)
Figure 9 - GS1 and GS2 Gain Ratios as a Function of Nominal Vdd
Gain Setting Resistor Calculation for Nominal Vdd between 3 and 5V
•
•
For the desired nominal Vdd, use Figure 9 to calculate approximate Av.
For the GS1 op-amp, start with the 0dB gain setting resistor values of R5 , R6
and R7 . In
0dB
0dB
0dB
Figure 8 they are 53K6, 60K4 and 464K respectively. Keep R1, R2, R3, R4, C1, C2 as in Figure 8 to
keep the input highpass filter corner frequency constant for all gain settings.
•
For the desired Av:
R7 = R7
x Av
Scaled for desired gain. Choose the closest standard 1%
resistor value as R7 . Calculate Av_actual as R7 /R7
Av
0dB
.
0dB
Av
Av
R5 = R5
x Av_actual
Scaled for good common mode range. Choose the closest
standard 1% resistor as R5 .
Av
0dB
Av
1/R6 = 1/R5 -1/R7
Calculate R6 so that R5 = R6 || R7 . Choose the
Av
Av
Av
Av Av Av Av
closest standard 1% resistor as R6 .
Av
•
Repeat for R10, R11 and R12 for the GS2 op-amp.
Example:
•
•
For the 3V gain of -4.0dB, Av = 0.63095.
R7 = 0.63095 x 464K = 292.76K. The closest standard 1% resistor is 294K.
-4dB
Av_actual is 294K/464K = 0.63362 or -3.96dB.
•
•
R5 = 0.63362 x 53K6 = 33.96K. The closest standard 1% resistor is 34K0.
-4dB
1/R6
= 1/34.0K - 1/294K = 1/38.45K. The closest standard 1% resistor is 38K3.
-4dB
13
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