Methods and apparatus to reduce variations for on-off keying transmissions

A system comprising:

• a level shifting circuit configured to generate a digital output based on a digital input, wherein voltage level of the digital output is shifter from voltage level of the digital input;
• and
• an on-off keying (OOK) modulator coupled to the level shifting circuit, circuit and comprising:
• a first transistor having a first terminal and a second terminal, wherein the first terminal is coupled to a first bias voltage;
• a second transistor having a third terminal and a fourth terminal, wherein the third terminal is coupled to a second bias voltage;
• and
• a third transistor having a control terminal coupled to the second terminal of the first transistor and the fourth terminal of the second transistor, wherein
• the OOK modulator configured to:
• turn on the first transistor to apply the first bias voltage to the control terminal of the third transistor in response to a first state of the digital output;
• turn on the second transistor to apply the second bias voltage to the control terminal of the third transistor in response to a second state of the digital output which is opposite to the first state;
• generate a current through the third transistor based on the voltage applied to the control terminal of the third transistor;
• and
• generate a modulated carrier signal based on an output of an oscillator and the current through the third transistor.

A method comprising:

• providing a first bias voltage at a control terminal of a transistor through a first transistor when a digital output is in a first state;
• providing a second bias voltage at the control terminal of the transistor through a second transistor when the digital output is in a second state;
• generating a current through the transistor based on voltage at the control terminal of the transistor;
• and
• generating a modulated carrier signal based on an output of an oscillator and the current through the transistor.