Variable frequency circuit controller
Apparatus and methods for distributing spurious tones through the frequency domain are disclosed. One such apparatus can include a dithering circuit configured to generate a sequence of numbers that exhibit statistical randomness and a variable frequency circuit configured to adjust a frequency of an output based on the sequence of numbers so as to spread energy of spurious tones in a frequency response of the output to lower a noise floor. In one example, spurious tones can be reduced in a negative voltage generator of a radio frequency (RF) attenuator.
1. An apparatus comprising:
a controller including a variable frequency circuit configured to spread energy of spurious tones through a frequency domain of a variable frequency signal, the controller configured to generate a control signal based on the variable frequency signal;
an attenuator component in communication with the controller, the attenuator component configured to attenuate a radio frequency (RF) signal based on the control signal; and
an amplifier configured to generate an RF output signal based on the attenuated RF signal, the amplifier, the controller, and the attenuator component being implemented on a single integrated circuit.
2. The apparatus of claim 1 wherein the controller includes a charge pump configured to generate a charge pump output based on the variable frequency signal, the control signal being based on the charge pump output.
3. An apparatus comprising:
a controller including a variable frequency circuit configured to spread energy of spurious tones through a frequency domain of a variable frequency signal, the controller being configured to generate a negative voltage based on the variable frequency signal and to generate a control signal based on the negative voltage; and
an attenuator component in communication with the controller, the attenuator component configured to attenuate a radio frequency (RF) signal based on the control signal.
4. The apparatus of claim 3 wherein the controller includes a level shifter configured to generate the control signal based on the negative voltage, the control signal being a differential signal.
5. The apparatus of claim 1 wherein the controller includes a dithering circuit in communication with the variable frequency circuit, the dithering circuit configured to generate an output sequence that exhibits statistical randomness.
6. The apparatus of claim 1 wherein the attenuator component is a digital step attenuator component.
7. The apparatus of claim 1 wherein the controller is a serial peripheral interface controller.
8. The apparatus of claim 3 further comprising an amplifier configured to generate an RF output signal based on the attenuated RF signal, and the amplifier, the controller, and the attenuator component being implemented on a single integrated circuit.
9. The apparatus of claim 1 further comprising either a low noise amplifier configured to provide the RF input signal to the attenuator component or a combiner configured to provide the RF input signal to the attenuator component.
10. An apparatus comprising a negative voltage generator configured to generate a negative voltage that is maintained below zero Volts, the negative voltage generator including a variable frequency circuit configured to generate an output having energy of spurious tones spread though the frequency domain, and the negative voltage generator including a charge pump in communication with the variable frequency circuit, the charge pump configured to generate the negative voltage based on the output of the variable frequency circuit.
11. The apparatus of claim 10 wherein the variable frequency circuit includes a variable oscillator.
12. The apparatus of claim 10 wherein the variable frequency circuit includes a fixed oscillator and a programmable divider.
13. The apparatus of claim 10 wherein the negative voltage generator further includes a buffer electrically coupled between the variable frequency circuit and the charge pump.
14. The apparatus of claim 10 further comprising a dithering circuit configured to provide an input sequence that exhibits statistical randomness to the variable frequency circuit.
15. The apparatus of claim 14 wherein a clock signal of the dithering circuit is based on the output of the variable frequency circuit.
16. An electronically-implemented method comprising:
distributing spurious tones through a frequency domain of a signal generated by a variable frequency circuit;
generating a negative voltage based on the signal generated by the variable frequency circuit; and
controlling attenuation of a radio frequency (RF) signal based on a differential signal that is generated using the negative voltage.
17. The method of claim 16 further comprising receiving an input sequence to the variable frequency circuit that exhibits statistical randomness, said distributing being based on the received input sequence.
18. The method of claim 17 further comprising generating the input sequence using a dithering circuit that includes a linear feedback shift register.
19. The method of claim 16 further comprising generating the differential signal based on an output word provided by control circuitry and the negative voltage.
20. The method of claim 19 further comprising generating the output word based on a serial bit stream received by the control circuitry.