Driver circuit
A line driver circuit for a High Definition Multimedia Interface (HDMI) transmitter is disclosed. The line driver circuit includes a pre-driver circuit having a pair of pre-driver differential inputs and a pair of pre-driver differential outputs. A driver circuit having a pair of driver differential inputs and a pair of driver differential outputs is also included. Each of the pair of pre-driver differential outputs is coupled to a respective one of the pair of driver differential inputs. Each of the pair of driver differential outputs is coupled to a respective one of a pair of output terminals. The pre-driver further includes a pair of pre-driver cascode transistors. Each of the pre-driver cascode transistors is arranged between one of the pre-driver differential outputs and a respective one of the output terminals and wherein the driver circuit and the pre-driver circuit are operable to receive a current supplied by a HDMI receiver coupled to the pair of output terminals.
1. A line driver circuit for a High Definition Multimedia Interface transmitter, the line driver circuit comprising:
a pre-driver circuit having a pair of pre-driver differential inputs and a pair of pre-driver differential outputs,
a driver circuit, having a pair of driver differential inputs and a pair of driver differential outputs,
wherein
each of the pair of pre-driver differential outputs is coupled to a respective one of the pair of driver differential inputs,
each of the pair of driver differential outputs is coupled to a respective one of a pair of output terminals, and
the pre-driver further comprises a pair of pre-driver cascode transistors, each of the pre-driver cascode transistors being arranged between one of the pre-driver differential outputs and a respective one of the output terminals and wherein the driver circuit and the pre-driver circuit are operable to receive a current supplied by a HDMI receiver coupled to the pair of output terminals.
2. The line driver circuit of claim 1 wherein the driver further comprises a pair of driver cascode transistors, and each of the driver cascode transistors is arranged between one of the driver differential outputs and a respective one of the output terminals and wherein the control terminals of the pair of driver cascode transistors are operably biased to a driver cascode bias voltage.
3. The line driver circuit of claim 1 wherein the control terminals of the pair of pre-driver cascode transistors are operably biased to a pre-driver cascode bias voltage.
4. The line driver circuit according to claim 1 wherein the driver circuit and pre-driver circuit each comprise a pair of transistors arranged as a long-tailed pair, each long-tailed pair transistor having a first terminal, a second terminal and a control terminal and wherein
each first terminal is coupled to a respective differential output,
each control terminal is coupled to a respective differential input,
the second terminals of each long-tailed pair transistor are coupled together and in operation the value of tail current in the driver circuit is greater than the value of the tail current in the pre-driver circuit.
5. The line driver circuit according to claim 3 further comprising a series resistance arranged between each of the control terminals of the pre-driver cascode transistors and a bias voltage supply.
6. The line driver circuit of claim 1 further comprising a further pre-driver circuit having a pair of further pre-driver differential inputs and a pair of further pre-driver differential outputs and wherein
each of the pair of further pre-driver differential outputs is coupled to a respective one of the pair of pre-driver differential inputs,
the further pre-driver comprises a pair of further pre-driver cascode transistors,
each of the further pre-driver cascode transistors being arranged between one of the further pre-driver differential outputs and a respective one of the output terminals, and wherein
in operation the further pre-driver circuit is arranged to receive a supply current from a HDMI receiver coupled to the pair of output terminals.
7. The line driver circuit according to claim 6 wherein the further pre-driver circuit comprises a pair of transistors arranged as a long-tailed pair, each long-tailed pair transistor having a first terminal, a second terminal and a control terminal and wherein
each first terminal is coupled to a respective one of the differential outputs,
each control terminal is coupled to a respective one of the differential inputs,
the second terminals of each long-tailed pair transistor are coupled together and
wherein in operation the value of tail current in the pre-driver circuit is greater than the value of the tail current in the further pre-driver circuit.
8. The line driver circuit according to claim 6 further comprising a series resistance arranged between each of the control terminals of the further pre-driver cascode transistors and a bias voltage supply.
9. The line driver circuit according to claim 1 , further comprising a first stage pre-driver coupled to a pre-driver and wherein the first stage pre-driver comprises:
a current mirror having a first current branch and a second current branch programmed by a reference current,
a first current switching transistor arranged in series with the first current branch, and
a second current switching transistor arranged in series with the second current branch; wherein
the first branch is coupled to a respective one of a pair of output terminals,
the second branch is coupled to the other of the pair of output terminals,
a first of the pair of further pre-driver differential inputs is coupled to the control terminal of the first current switching transistor,
a second of the pair of further pre-driver differential inputs is coupled to the control terminal of the second current switching transistor and
the first stage pre-driver is operable to receive a current supplied by a HDMI receiver coupled to the pair of output terminals when either of the first or second current switching transistors is enabled.
10. The line driver circuit according to claim 1 wherein the total value of the current drawn is in the range of 9 mA to 20 mA.
11. An HDMI transmitter comprising the line driver circuit of claim 1 .
12. A HDMI level shifter comprising the line driver circuit of claim 1 .
13. An integrated circuit comprising the line driver circuit according to claim 1 .
14. A mobile hand held device comprising the integrated circuit of claim 13 wherein the mobile hand held device comprises one of a mobile phone, a tablet computer, a digital camera, a laptop computer.