Comparator with sensitivity control
View Patent ↗A comparator has a differential input stage, a current source coupled to the differential input stage for providing a tail current to one side of the differential input stage, and a differential load coupled to the differential pair and having at least one diode coupled load transistor per differential side. A load current through either one of the at least one diode coupled load transistor on either differential side is mirrored with a current mirror configuration to provide a current be fed to a respective node, each node being coupled to a respective variable biasing current source and a respective other side of the differential input stage, so as to provide a variable positive feedback to the differential input stage.
1. A comparator for demodulating an amplitude modulated RF signal received in an RFID transponder, the comparator comprising:
a differential input stage (MN 1 , MN 2 ),
a current source (Iscr) coupled to the differential input stage (MN 1 , MN 2 ) for providing a tail current (I 9 ) to the differential input stage (MN 1 , MN 2 ), and
a differential load coupled to the differential input stage and comprising at least one diode coupled load transistor (MP 3 , MP 4 ) per differential side, wherein
a load current (I 3 , I 4 ) through either one of the at least one diode coupled load transistor (MP 3 , MP 4 ) on either differential side is mirrored out with a current mirror configuration having a factor A to provide a current (I 6 , I 7 ) be fed to a respective node (N 1 , N 2 ), each node (N 1 , N 2 ) being coupled to a respective variable biasing current source and a respective other side of the differential input stage (MN 1 , MN 2 ), so as to provide a variable positive feedback to the differential input stage (MN 1 , MN 2 ).
2. The comparator according to claim 1 , wherein the variable biasing current source comprises two transistors (MN 8 , MN 9 ) having their gates coupled together for being commonly controlled by a control voltage (Bias_I cntl ).
3. The comparator according to claim 1 , wherein the current mirror configuration is established by coupling two transistors (MP 6 , MP 7 ) with their gates to the gates of the diode coupled load transistors.
4. A RFID transponder comprising:
an antenna;
a demodulator comprising:
a differential input stage having a differential load having at least one diode coupled transistor coupled to a differential pair of transistors, a load current through either one of the at least one diode coupled transistor being mirrored by a current mirror having a current ration of 1:A to provide current to a respective node, each node being coupled to a respective variable biasing current source and a respective other side of the differential input stage, whereby a variable positive feedback to the differential input stage is provided.
5. The transponder of claim 4 further comprising a current source coupled to the differential input stage providing a tail current.
6. The transponder of claim 4 , wherein the variable biasing current source comprises two transistors (MN 8 , MN 9 ) having their gates coupled together for being commonly controlled by a control voltage (Bias_I cntl ).
7. The transponder of claim 5 , wherein the variable biasing current source comprises two transistors (MN 8 , MN 9 ) having their gates coupled together for being commonly controlled by a control voltage (Bias_I cntl ).
8. The transponder of claim 3 , wherein the current mirror configuration is established by coupling two transistors (MP 6 , MP 7 ) with their gates to the gates of the diode coupled load transistors.
9. The transponder of claim 4 , wherein the current mirror configuration is established by coupling two transistors (MP 6 , MP 7 ) with their gates to the gates of the diode coupled load transistors.
10. The transponder of claim 5 , wherein the current mirror configuration is established by coupling two transistors (MP 6 , MP 7 ) with their gates to the gates of the diode coupled load transistors.
11. The transponder of claim 6 , wherein the current mirror configuration is established by coupling two transistors (MP 6 , MP 7 ) with their gates to the gates of the diode coupled load transistors.
12. The transponder of claim 7 , wherein the current mirror configuration is established by coupling two transistors (MP 6 , MP 7 ) with their gates to the gates of the diode coupled load transistors.
13. A comparator for demodulating an amplitude modulated RF signal received in an RFID transponder, the comparator comprising:
a differential input stage (MN 1 , MN 2 ),
a current source (Iscr) coupled to the differential input stage (MN 1 , MN 2 ) for providing a tail current (I 9 ) to the differential input stage (MN 1 , MN 2 ); and
a differential load coupled to the differential input stage and comprising at least one diode coupled load transistor (MP 3 , MP 4 ) per differential side, wherein
a load current (I 3 , I 4 ) through either one of the at least one diode coupled load transistor (MP 3 , MP 4 ) on either differential side is mirrored with a current mirror configuration having a factor A to provide a current (I 6 , I 7 ) be fed to a respective node (N 1 , N 2 ), each node (N 1 , N 2 ) being coupled to a respective variable biasing current source and a respective other side of the differential input stage (MN 1 , MN 2 ), so as to provide a variable positive feedback to the differential input stage (MN 1 , MN 2 );
wherein the variable biasing current source comprises two transistors (MN 8 , MN 9 ) having their gates coupled together for being commonly controlled by a control voltage (Bias_I cntl ); and the current mirror configuration is established by coupling two transistors (MP 6 , MP 7 ) with their gates to the gates of the diode coupled load transistors.