Rail-to-rail line driver using differential cascode bootstraping
View Patent ↗Aspects of rail-to-rail line drivers using differential cascode bootstrapping are described. In one embodiment, a differential line driver includes first and second differential driver output legs. The first output leg includes a first p-type cascode stack and a first n-type cascode stack, and the second output leg includes a second p-type cascode stack and a second n-type cascode stack. The differential line driver also includes a differential cascode bootstrap circuit arrangement coupled to an output of the differential line driver. More particularly, the differential cascode bootstrap circuit arrangement is coupled between the first and second differential output driver legs and the output of the differential line driver. According to aspects of the embodiments described herein, differential line drivers with overvoltage protection and rail-to-rail output swings may be achieved. Further, the differential line drivers may be generally smaller, with cascode stack transistors of reduced in size.
1. A differential line driver, comprising:
a first differential driver output leg comprising a first p-type cascode stack and a first n-type cascode stack;
a second differential driver output leg comprising a second p-type cascode stack and a second n-type cascode stack; and
a differential cascode bootstrap circuit arrangement coupled to an output of the differential line driver,
wherein the cascode bootstrap circuit includes a first passive impedance circuit path and a second passive impedance circuit path.
2. The differential line driver according to claim 1 , wherein the differential cascode bootstrap circuit arrangement is coupled between the first and second differential driver output legs and the output of the differential line driver.
3. The differential line driver according to claim 1 , wherein:
the first p-type cascode stack includes a first plurality of p-type transistors including at least a first thin oxide p-type transistor and a first thick oxide p-type transistor; and
the first n-type cascode stack including a first plurality of n-type transistors including at least a first thin oxide n-type transistor and a first thick oxide n-type transistor.
4. The differential line driver according to claim 3 , wherein the first passive impedance circuit path is coupled between gates of the first thick oxide p-type transistor and the first thick oxide n-type transistor and an output of the second differential driver output leg.
5. The differential line driver according to claim 1 , wherein:
the second p-type cascode stack including a second plurality of p-type transistors including at least a second thin oxide p-type transistor and a second thick oxide p-type transistor; and
the second n-type cascode stack including a second plurality of n-type transistors including at least a second thin oxide n-type transistor and a second thick oxide n-type transistor.
6. The differential line driver according to claim 5 , wherein the second passive impedance circuit path is coupled between gates of the second thick oxide p-type transistor and the second thick oxide n-type transistor and an output of the first differential driver output leg.
7. The differential line driver according to claim 1 , further comprising:
a first current mirror leg including a first p-type cascode mirror stack and a first n-type cascode mirror stack; and
a second current mirror leg including a second p-type cascode mirror stack and a second n-type cascode mirror stack.
8. The differential line driver according to claim 7 , further comprising:
a first difference amplifier coupled between the first differential driver output leg and the first current mirror leg; and
a second difference amplifier coupled between the second differential driver output leg and the second current mirror leg.
9. The differential line driver according to claim 1 , wherein both the first and the second passive impedance circuit paths include at least one of a resistive element and a capacitive element.
10. A differential line driver, comprising:
a first differential driver output leg comprising a first cascode stack;
a second differential driver output leg comprising a second cascode stack; and
a differential cascode bootstrap circuit coupled between the first and second differential output driver legs and the output of the differential line driver, the differential cascode bootstrap circuit including a first passive impedance circuit path and a second passive impedance circuit path.
11. The differential line driver according to claim 10 , wherein:
the first differential driver output leg includes a first p-type cascode stack and a first n-type cascode stack; and
the second differential driver output leg includes a second p-type cascode stack and a second n-type cascode stack.
12. The differential line driver according to claim 11 , wherein:
the first p-type cascode stack includes a first plurality of p-type transistors including at least a first thin oxide p-type transistor and a first thick oxide p-type transistor; and
the first n-type cascode stack includes a first plurality of n-type transistors including at least a first thin oxide n-type transistor and a first thick oxide n-type transistor.
13. The differential line driver according to the claim 12 , wherein the first passive impedance circuit path is coupled between gates of the first thick oxide p-type transistor and the first thick oxide n-type transistor and an output of the second differential driver output leg.
14. The differential line driver according to the claim 11 , wherein:
the second p-type cascode stack includes a second plurality of p-type transistors including at least a second thin oxide p-type transistor and a second thick oxide p-type transistor; and
the second n-type cascode stack includes a second plurality of n-type transistors including at least a second thin oxide n-type transistor and a second thick oxide n-type transistor.
15. The differential line driver according to the claim 14 , wherein the second passive impedance circuit path is coupled between gates of the second thick oxide p-type transistor and the second thick oxide n-type transistor and an output of the first differential driver output leg.
16. The differential line driver according to the claim 10 , further comprising:
a first current mirror leg including a first p-type cascode mirror stack and a first n-type cascode mirror stack; and
a second current mirror leg including a second p-type cascode mirror stack and a second n-type cascode mirror stack.
17. The differential line driver according to the claim 16 , further comprising:
a first difference amplifier coupled between the first differential driver output leg and the first current mirror leg; and
a second difference amplifier coupled between the second differential driver output leg and the second current mirror leg.
18. A differential driving method, comprising:
driving a first voltage on a first differential output node of a differential line driver;
driving a second voltage on a second differential output node of the differential line driver; and
differentially bootstrapping the first and second differential output nodes of the differential line driver to gate terminals of cascode transistors of a differential cascode bootstrap circuit of the differential line driver, the differentical cascode bootstrap circuit including a first passive impedance circuit path and a second passive impedance circuit path.
19. The differential driving method according to claim 18 , further comprising mirroring drain to source operating voltage differentials across transistors in the differential line driver to transistors of a local loop current mirror.
20. The differential driving method according to claim 18 , wherein the differentially bootstrap includes differential line driver comprises:
differentially bootstrap an output of a first differential driver output leg comprising a first p-type cascode stack and a first n-type cascode stack, the output of the first differential driver output leg corresponding to the first output node; and
differentially bootstrapping an output of a second differential driver output leg comprising a second p-type cascode stack and a second n-type cascode stack, the output of the second differential driver output leg corresponding to the second output node.