spatial bandpass filter

Which is commonly usedin computer vision to findvisual "edges" to determinethe shape of objects.

Vf

Vout

Iphoto

Vf

Vout

Iphoto

High gain inverting amp

Vout drops logarithmically with Iphoto

Vf

Vout

Iphoto

High gain inverting amp

Vp

C1

R

By closing the loop, we can make this adaptive.

Vout

IphotoVp

If the loop is closed, we have our familiar circuit which has Vout =

2ln( ) ln( )

T bias T photo

o o

V I V IVout

K I K I

1TVout V

Iphoto K Iphoto

Because the ac gain of the amplifier is very high, in practice, itis better to limit the gain using a capacitor divider.

Vf

Vout

Iphoto

High gain inverting amp

Vp

C1

R

C2

1 2 1

2

TVout V C C

Iphoto K Iphoto C

Since Vout now does the same job of feedback through the capacitor divider,

Delbruck and Mead Photoreceptor