B.V.RAJU INSTITUTE OF TECHNOLOGY

Vishnupur , Narsapur , Medak (Dt)

(Affiliated to JNTU, Hyderabad)

2015

Technical Seminar

On

PRESENTED

BY

R.MANIKANTA

(14211D5707)

Definition Of CMRR?

CMRR=Adm/Acm

How to introduce noise in

CMRR

What is Gyrator??

o A 180 degrees phase shift occurs for signals traveling from

port-1 to port-2 and zero phase shift occurs for a signals

traveling from port-2 to port-1.

INTRODUCTION

As for differential signal transfer in these filter circuits,

it is important to consider normal/common-mode noise.

For the common-mode noise rejection, the filter circuits

generally applied a differential amplifier with a common-

mode feedback (CMFB) scheme

FCMFB scheme

Active inductor with gyrator-C network.

Floating active transformer.

Gm amplifiers consist of the CMFB scheme with common

resistances.

The CMFB scheme keeps the DC voltage of the output

constant

In this circuit, the DC levels of the input/output should be

lower/higher than half of the VDD

By adding Gm amplifiers, Gm3, to the ladder

structure, we can reduce common-mode noise.

It is shown in fig floating active transformer.

Each port of the differential signal is inverted and connected

to the opposite side

Half part of floating active transformer.

- I1 + V3Gm2 =0: node 1;

- I2 + V4Gm2 = 0: node 2;

sCV3 -V1Gm1 + V2Gm3 = 0: node 3;

sCV4 - V2Gm1 + V1Gm3 = 0: node 4;

V1 = sL11I1 + sM12I2 =

sCI1

+

sCI2

Gm2Gm3_ Gm1Gm2_

V2 = sL22I2 + sM21I1 =

sCI2

+

sCI1

Gm2Gm3_ Gm1Gm2_

L11 = L22 =

C

; M12 = M21 =

C

Gm2Gm3_Gm1Gm2

_

_ Del

=

Gm12 _-Gm3

2

/Gm1Gm3

When we set a larger equivalent mutual conductance, more

noise reduction can be achieved.

we can control the mutual inductance M and the inductance

Lby changes of the parameter Gmx. When Gm3 increases, M

increases

Circuit configuration of 6th order LC-ladder LPF with common-mode noise

reduction.

Using this active transformer, simultaneous LC-ladder filter

operation and common-mode noise reduction is possible.

Conclusion

References

THANK YOU