current mirror

Current mirror

So before going to the band gap reference we learn what is current mirror?

current mirror as the name suggest it analogous to simple mirror which reflect light from the one mirror to other it reflect the light in the similar fashion a current mirror reflect the current from the current source to other terminal.

light analogy

i think commit a mistake both transistor should be pnp 

so what is ideal current mirror?

ideal current mirror have infinite output resistance  and also ideal current mirror is simply an ideal inverting current amplifier that reverses the current direction as well or it is a current-controlled current source (CCCS).ideally output current is input current and multiplied to the desired current gain value.furthermore ,the voltage between the input and common terminal is ideally zero because this condition allow entire supply voltage appear across the input current source also ideal  current source  should be independent of frequency.

where CCCS means the current source whose value is controlled some other component ,bjt is also CCCS .

Deviation from ideal current mirror?

1)the variation of the current mirror output current with change in voltage at the output terminal.this is due to the output resistance (Ro),of the current mirror

2)gain error :-1) systematic gain error : this error even occur  all the element of transistor is perfectly matched,we will go through this in further blog.

                2)random error:-this occurs due to the mismatch in the element values.

3)voltage headroom: it is minimum voltage vout (output voltage) should lie above the minimum voltage required to transistor remain in active region where it act as current source .

vin (input voltage) should also be less so that max voltage across the reference current source.

So going further there are several form of design in current mirror and every type have there own short coming and profits  to be continued in next blog ...........

Current mirror

So before going to the band gap reference we learn what is current mirror?

current mirror as the name suggest it analogous to simple mirror which reflect light from the one mirror to other it reflect the light in the similar fashion a current mirror reflect the current from the current source to other terminal.

light analogy

i think commit a mistake both transistor should be pnp 

so what is ideal current mirror?

ideal current mirror have infinite output resistance  and also ideal current mirror is simply an ideal inverting current amplifier that reverses the current direction as well or it is a current-controlled current source (CCCS).ideally output current is input current and multiplied to the desired current gain value.furthermore ,the voltage between the input and common terminal is ideally zero because this condition allow entire supply voltage appear across the input current source also ideal  current source  should be independent of frequency.

where CCCS means the current source whose value is controlled some other component ,bjt is also CCCS .

Deviation from ideal current mirror?

1)the variation of the current mirror output current with change in voltage at the output terminal.this is due to the output resistance (Ro),of the current mirror

2)gain error :-1) systematic gain error : this error even occur  all the element of transistor is perfectly matched,we will go through this in further blog.

                2)random error:-this occurs due to the mismatch in the element values.

3)voltage headroom: it is minimum voltage vout (output voltage) should lie above the minimum voltage required to transistor remain in active region where it act as current source .

vin (input voltage) should also be less so that max voltage across the reference current source.

So going further there are several form of design in current mirror and every type have there own short coming and profits  to be continued in next blog ...........