关于运放的共模抑制比
当输入均是V 时，输出V out 的电压值是：
V out R 3R 2-R 1R 4 =V cm (R 1+R 3) R 2
单端输入时：
V out R 3R 2+R 3R 4 =V d (R 1+R 3) R 2
共模抑制比是：
K cmr =20lg A d A c
R 3R 2+R 3R 4 R 3R 2-R 1R 4K cmr =20lg
如果R 3= R4，R 2 = R1，V out = 0
放大倍率为1，但如果每个电阻使用0.5%的电阻，Matlab 计算结果最坏的情况下： r1 = 10000;
r2 = 10000;
r3 = 10000;
r4 = 10000;
alpha = 0.5 / 100;
CMmax = -1000;
CMmin = 1000;
Dmax = -1000;
Dmin = 1000;
Kcmrmax = -100000;
Kcmrmin = 100000;
for rr1=[r1*(1-alpha) r1 r1 * (1+alpha)]
for rr2=[r2*(1-alpha) r2 r2 * (1+alpha)]
for rr3=[r3*(1-alpha) r3 r3 * (1+alpha)]
for rr4=[r4*(1-alpha) r4 r4*(1+alpha)]
Cratio = (rr3 * rr2 - rr1 * rr4) / (rr1 + rr3) / rr2; Dratio = (rr3 * rr2 + rr3 * rr4) / (rr1 + rr3) / rr2; Kcmr = 20 * log10(abs(Dratio/Cratio));
if (Cratio > CMmax)
CMmax = Cratio;
end
if (Cratio
CMmin = Cratio;
end
if (Dratio > Dmax)
Dmax = Dratio;
end
if (Dratio
Dmin = Dratio;
end
if (Kcmr > Kcmrmax)
Kcmrmax = Kcmr;
end
if (Kcmr
Kcmrmin = Kcmr;
end
end
end
end
end
CMmax,CMmin,Dmax,Dmin, Kcmrmax, Kcmrmin
计算结果：
CMmax = 0.0100
CMmin = -0.0101
Dmax = 1.0101
Dmin = 0.9900
Kcmrmax = Inf (无穷大)
Kcmrmin = 39.9565 dB
最差的情况下，如果有1V 的共模，将在输出端最大产生10mV (或-10mV) 的电压。
关于运放的共模抑制比
当输入均是V 时，输出V out 的电压值是：
V out R 3R 2-R 1R 4 =V cm (R 1+R 3) R 2
单端输入时：
V out R 3R 2+R 3R 4 =V d (R 1+R 3) R 2
共模抑制比是：
K cmr =20lg A d A c
R 3R 2+R 3R 4 R 3R 2-R 1R 4K cmr =20lg
如果R 3= R4，R 2 = R1，V out = 0
放大倍率为1，但如果每个电阻使用0.5%的电阻，Matlab 计算结果最坏的情况下： r1 = 10000;
r2 = 10000;
r3 = 10000;
r4 = 10000;
alpha = 0.5 / 100;
CMmax = -1000;
CMmin = 1000;
Dmax = -1000;
Dmin = 1000;
Kcmrmax = -100000;
Kcmrmin = 100000;
for rr1=[r1*(1-alpha) r1 r1 * (1+alpha)]
for rr2=[r2*(1-alpha) r2 r2 * (1+alpha)]
for rr3=[r3*(1-alpha) r3 r3 * (1+alpha)]
for rr4=[r4*(1-alpha) r4 r4*(1+alpha)]
Cratio = (rr3 * rr2 - rr1 * rr4) / (rr1 + rr3) / rr2; Dratio = (rr3 * rr2 + rr3 * rr4) / (rr1 + rr3) / rr2; Kcmr = 20 * log10(abs(Dratio/Cratio));
if (Cratio > CMmax)
CMmax = Cratio;
end
if (Cratio
CMmin = Cratio;
end
if (Dratio > Dmax)
Dmax = Dratio;
end
if (Dratio
Dmin = Dratio;
end
if (Kcmr > Kcmrmax)
Kcmrmax = Kcmr;
end
if (Kcmr
Kcmrmin = Kcmr;
end
end
end
end
end
CMmax,CMmin,Dmax,Dmin, Kcmrmax, Kcmrmin
计算结果：
CMmax = 0.0100
CMmin = -0.0101
Dmax = 1.0101
Dmin = 0.9900
Kcmrmax = Inf (无穷大)
Kcmrmin = 39.9565 dB
最差的情况下，如果有1V 的共模，将在输出端最大产生10mV (或-10mV) 的电压。