Circuit and method for body biasing
Various example embodiments are directed to methods and circuits for mitigation of on-resistance variation and signal attenuation in transistors due to body effects. In some embodiments, an apparatus includes a transistor configured to provide a data signal from a first one of the source or the drain to the other one of the source or the drain in response to a control signal provided to the gate. A body bias circuit is configured to bias the body of the transistor based on a voltage of the data signal to reduce variation in the on-resistance exhibited by the first transistor. In an embodiment, the apparatus includes body bias transistors and switches and the gates of the body bias transistors are connected to protect the body bias transistors from the effects of electrostatic discharge (ESD) events.
1. An apparatus, comprising:
a first transistor having a source, a drain, a gate, and a body, the first transistor configured and arranged to provide a data signal from a first one of the source or the drain to the other one of the source or the drain in response to a control signal provided to the gate, the first transistor being subject to attenuation of the data signal due to body effects; and
a body bias circuit configured and arranged to bias the body of the first transistor based on a voltage of the data signal and to reduce attenuation of the data signal by the first transistor, wherein the body bias circuit includes:
a second transistor having a source, a drain, and a gate and wherein the source and drain are connected between the body of the first transistor and the first one of the source or the drain of the first transistor;
a third transistor having a source, a drain, and a gate and wherein the source and drain are connected between the body of the first transistor and the other one of the source or drain of the first transistor;
the apparatus further including:
a first switch connected between the second transistor and the first one of the source or the drain of the first transistor;
a second switch connected between the third transistor and the other one of the source or the drain of the first transistor;
wherein the gate of the second transistor is connected between the second switch and the third transistor and the gate of the third transistor is connected between the first switch and the second transistor.
2. The apparatus of claim 1 , wherein:
the first transistor is an n-type transistor subject to variation in on-resistance between the source and drain for different voltages of the data signal due to body effects; and
the body bias circuit is configured and arranged to bias the body of the first transistor toward the lesser of a source voltage of the source and a drain voltage of the drain, thereby reducing variation in the on-resistance exhibited by the first transistor.
3. The apparatus of claim 2 , wherein:
the body bias circuit is configured and arranged to
in response to the drain voltage being less than the source voltage, bias the body of the first transistor toward the drain voltage of the drain; and
in response to the source voltage being less than the drain voltage, bias the body of the first transistor toward the source voltage.
4. The apparatus of claim 2 , wherein:
the second transistor is configured and arranged to connect the body of the first transistor to the drain of the first transistor in response to the drain voltage being less than the source voltage; and
the third transistor is configured and arranged to connect the body of the first transistor to the source of the first transistor in response to the drain voltage being greater than the source voltage.
5. The apparatus of claim 1 , wherein:
the first transistor is a p-type transistor subject to variation in on-resistance between the source and drain for different voltages of the data signal due to body effects; and
the body bias circuit is configured and arranged to bias the body of the first transistor toward the greater of a source voltage of the source and a drain voltage of the drain, thereby reducing variation in the on-resistance exhibited by the first transistor.
6. The apparatus of claim 5 , wherein:
the body bias circuit is configured and arranged to
in response to drain voltage being greater than the source voltage, bias the body of the first transistor toward the drain voltage; and
in response to the source voltage being greater than the drain voltage, bias the body of the first transistor toward the source voltage.
7. The apparatus of claim 6 , wherein:
the second transistor is configured and arranged to connect the body of the first transistor to the drain of the first transistor in response to the drain voltage being greater than the source voltage; and
the third transistor is configured and arranged to connect the body of the first transistor to the source of the first transistor in response to the drain voltage being less than the source voltage.
8. The apparatus of claim 1 , wherein the body bias circuit is configured and arranged to bias the body of the first transistor to follow a voltage of the data signal.
9. An apparatus, comprising:
a first transistor having a source, a drain, a gate, and a body, wherein the transistor is subject to variation in on-resistance between the source and drain for different voltages of an input data signal due to body effects; and
a body bias circuit configured and arranged to bias the body of the first transistor to reduce variation in the on-resistance exhibited by the first transistor, thereby reducing attenuation of the input data signal;
the body bias circuit including:
a second transistor having a source, a drain, and a gate and wherein the source and drain are connected between the body of the first transistor and the first one of the source or the drain of the first transistor;
a third transistor having a source, a drain, and a gate and wherein the source and drain are connected between the body of the first transistor and the other one of the source or drain of the first transistor;
the apparatus further including:
a first switch connected between the second transistor and the first one of the source or the drain of the first transistor;
a second switch connected between the third transistor and the other one of the source or the drain of the first transistor;
wherein the gate of the second transistor is connected between the second switch and the third transistor and the gate of the third transistor is connected between the first switch and the second transistor.
10. The apparatus of claim 9 , further comprising
a switch including the first transistor and having an input/output node connected to the drain, an output/input node connected to the source, and a control node connected to the gate, the switch being configured and arranged to communicate the input data signal between the input/output node and the output/input node in response to the control node exceeding a threshold voltage; and
wherein the body bias circuit is configured to bias the body of the first transistor to follow the input data signal.
11. The apparatus of claim 9 , wherein:
the first transistor is an n-type transistor; and
the body bias circuit is configured and arranged to bias the body of the first transistor toward the lesser of a source voltage of the source and a drain voltage of the drain.
12. The apparatus of claim 9 , wherein:
the first transistor is an n-type transistor; and
the second transistor is configured and arranged to connect the body of the first transistor to the drain of the first transistor in response to the drain voltage being less than the source voltage, and
the third transistor is configured and arranged to connect the body of the first transistor to the source of the first transistor in response to the drain voltage being greater than the source voltage of the source.
13. The apparatus of claim 9 , wherein:
the first transistor is a p-type transistor; and
the second transistor is configured and arranged to connect the body of the first transistor to the drain of the first transistor in response to the drain voltage being greater than the source voltage, and
the third transistor is configured and arranged to connect the body of the first transistor to the source of the first transistor in response to the drain voltage being less than the source voltage of the source.
14. A method, comprising:
communicating a data signal between a source of a transistor and a drain of the transistor in response to a control signal, the transistor being subject to attenuation of the data signal due to body effects;
biasing, based on a voltage of the data signal, a body of the transistor to reduce attenuation of the data signal by the transistor; and
disconnecting the gate of a body bias transistor from one of the source or the drain of the transistor by opening a switch, wherein the gate of the body bias transistor is connected between one of the source or drain of the transistor and one of the source or drain of the body bias transistor.
15. The method of claim 14 , wherein:
the transistor is an n-type transistor; and
the biasing the body includes biasing the body toward the lesser of a source voltage of the source and a drain voltage of the drain.
16. The method of claim 15 , wherein the biasing the body includes:
in response to the drain voltage being less than the source voltage, biasing the body of the transistor toward the drain voltage of the drain; and
in response to the source voltage being less than the drain voltage, biasing the body of the transistor toward the source voltage.
17. The method of claim 16 , wherein:
the biasing the body of the transistor toward the drain voltage of the drain includes connecting the body to the drain; and
the biasing the body of the transistor toward the drain voltage of the drain includes connecting the body to the source.
18. The method of claim 14 , wherein:
the transistor is a p-type transistor; and
in response to a drain voltage of the drain being greater than a source voltage of the source, biasing the body of the transistor toward the drain voltage of the drain; and
in response to the source voltage being greater than the drain voltage, biasing the body of the transistor toward the source voltage.
19. An apparatus, comprising:
a first transistor having a source, a drain, a gate, and a body, the first transistor configured and arranged to provide a data signal from an input to an output in response to a control signal provided to the gate, the first transistor being subject to attenuation of the data signal due to body effects;
a body bias circuit configured and arranged to bias the body of the first transistor based on a voltage of the data signal and to reduce attenuation of the data signal by the first transistor, wherein the body bias circuit includes:
a first body bias transistor having a source, a drain, and a gate and wherein the source and drain are connected between the body of the first transistor and input of the first transistor;
a second body bias transistor having a source, a drain, and a gate and wherein the source and drain are connected between the body of the first transistor and the output of the first transistor;
the apparatus further including:
a first switch connected between the first body bias transistor and the input of the first transistor;
a second switch connected between the second body bias transistor and the output of the first transistor;
wherein the gate of the first body bias transistor is connected between the second switch and the second body bias transistor and the gate of the second body bias transistor is connected between the first switch and the first body bias transistor.