Apparatus including a bias voltage generator
An apparatus comprising: a cascode arrangement comprising two or more transistors, the cascode arrangement coupled between a supply voltage terminal for receiving a supply voltage from a battery and a ground terminal, and a bias voltage generator configured to provide a bias voltage to at least one of the two or more transistors of the cascode arrangement to bias the cascode arrangement, the bias voltage generator further configured to increase the bias voltage with increasing supply voltage at a first rate over a first supply voltage range and increase the bias voltage with increasing supply voltage at a second rate, greater than the first rate, over a second supply voltage range, wherein the second supply voltage range comprises a range of voltages greater than the first supply voltage range.
1 . An apparatus comprising,
a cascode arrangement comprising two or more transistors, the cascode arrangement coupled between a supply voltage terminal for receiving a supply voltage from a battery and a ground terminal, and
a bias voltage generator configured to provide a bias voltage to at least one of the two or more transistors of the cascode arrangement to bias the cascode arrangement, the bias voltage generator further configured to at least increase the bias voltage with increasing supply voltage at a first rate over a first supply voltage range and increase the bias voltage with increasing supply voltage at a second rate, greater than the first rate, over a second supply voltage range, wherein the second supply voltage range comprises a range of voltages greater than the first supply voltage range.
2 . An apparatus according to claim 1 , wherein the cascode arrangement comprises at least three transistors comprising:
a first transistor having a first terminal, a second terminal and a control terminal, the first terminal of the first transistor configured to couple to the supply voltage terminal;
a second transistor having a first terminal, a second terminal and a control terminal, the first terminal of the second transistor coupled to the second terminal of the first transistor; and
a third transistor having a first terminal, a second terminal and a control terminal, the first terminal of the third transistor coupled to the second terminal of the second transistor and the second terminal of the third transistor is configured to be coupled to the ground terminal; and wherein
the bias voltage generator is configured to provide the bias voltage to one or both of the control terminal of the first transistor and the control terminal of the second transistor.
3 . An apparatus according to claim 2 , wherein
the bias voltage increases monotonically with respect to the supply voltage over the first supply voltage range.
4 . An apparatus according to claim 2 , wherein
the bias voltage increases monotonically with respect to the supply voltage over the second supply voltage range.
5 . An apparatus according to claim 2 , wherein
the first supply voltage range comprises a voltage range between 2V and 4V.
6 . An apparatus according to claim 2 , wherein
the second supply voltage range comprises a voltage range above 3.5V.
7 . An apparatus according to claim 1 , wherein
the bias voltage increases monotonically with respect to the supply voltage over the first supply voltage range.
8 . An apparatus according to claim 1 , wherein
the bias voltage increases monotonically with respect to the supply voltage over the second supply voltage range.
9 . An apparatus according to claim 1 , wherein
the first supply voltage range comprises a voltage range between 2V and 4V.
10 . An apparatus according to claim 1 , wherein
the second supply voltage range comprises a voltage range above 3.5V.
11 . An apparatus according to claim 1 , wherein
the first supply voltage range and the second supply voltage range are non-overlapping and contiguous with one another.
12 . An apparatus according to claim 1 , wherein
the bias voltage generator is configured to provide the bias voltage such that the voltage difference between the supply voltage terminal and the bias voltage is below a predetermined threshold in at least the second supply voltage range.
13 . An apparatus according to claim 1 , wherein
the bias voltage generator further comprises at least two current source arrangements, and wherein
the at least two current source arrangements comprise:
a first current source arrangement configured to provide a first output current dependent on the supply voltage according to a first function; and
a second current source arrangement configured to provide a second output current dependent on the supply voltage according to a second function, different to the first function; and
the bias voltage generator further comprises a current to voltage converter configured to generate the bias voltage, wherein the bias voltage is based on a sum of the first current and the second current provided to the current to voltage converter by the at least two current source arrangements.
14 . An apparatus according to claim 13 , wherein
the first output current being dependent on the supply voltage according to the first function comprises the first current source arrangement being configured to provide the first output current such that it increases with increasing supply voltage.
15 . An apparatus according to claim 13 , wherein
the second output current being dependent on the supply voltage according to the second function comprises the second current source arrangement configured to provide the second output current such that it increases with increasing supply voltage, wherein the second output current is only provided above a nominal level after a threshold supply voltage set point is reached, wherein the threshold supply voltage set point is greater than zero.
16 . An apparatus according to claim 13 , wherein
the first current source arrangement comprises a temperature dependent current source and a supply voltage dependent current source, configured to provide the first output current, and
the second current source arrangement comprises a temperature dependent current source and a supply voltage dependent current source, configured to provide the second output current.
17 . An apparatus according to claim 13 , wherein
the first current source arrangement is configured such that the relationship between the first output current and the supply voltage is substantially linear, and
the second current source arrangement is configured such that the relationship between the second output current and the supply voltage is substantially non-linear.
18 . An apparatus according to claim 13 , wherein
the current to voltage converter comprises:
a resistor coupled between the control terminal of the first transistor of the cascode arrangement and the supply voltage terminal;
at least one transistor coupled between the control terminal of the first transistor of the cascode arrangement and the ground terminal; and wherein
the output of the current to voltage converter is based on the voltage drop across the resistor and a base-emitter voltage of the at least one transistor of the current to voltage converter.
19 . An apparatus according to claim 13 , wherein the supply voltage is provided by a rechargeable battery.
20 . An apparatus according to claim 1 , wherein the supply voltage is provided by a rechargeable battery.