On page 1146 in the third paragraph you indicate that you can't use

the topology seen in Fig. 31.19 for the TIA because it's not inverting.

However, if the input current goes up the output voltage goes down so

isn't it inverting?


Yes, you are right and this is a good question. The reason you can't use

this topology is that the reset device, M5 in Fig. 31.51, must be connected

between a high-impedance node and a low-impedance node for the reset to

work properly. This means that the reset device can't be connected back to

the input in Fig. 31.19.


The key thing is that M5 can't have a DC current flowing in it if the reset

is to work correctly. If M5 does pass a current then the biasing will be

corrupted when M5 shuts off causing the amplifier's output to move towards

either vdd or gnd.