Envelope tracking voltage tracker circuit and related power management circuit
An envelope tracking (ET) voltage tracker circuit and related power management circuit are provided. In examples discussed herein, an amplifier circuit(s) is configured to amplify a radio frequency (RF) signal(s) based on an ET modulated voltage provided by an ET voltage tracker circuit(s). The ET voltage tracker circuit(s) includes amplifier circuitry, which operates based on an ET target voltage and a bias current to generate the ET modulated voltage. However, the ET modulated voltage may deviate from the ET target voltage from time to time due to cross over distortions. In this regard, the ET voltage tracker circuit includes a bias modulation circuit to dynamically determine the cross over distortion and adjust the bias current to reduce deviations of the ET modulated voltage. As a result, the ET modulated voltage can track the ET target voltage more closely, thus helping to improve linearity performance and efficiency of the amplifier circuit(s).
1. An envelope tracking (ET) voltage tracker circuit comprising:
amplifier circuitry comprising a voltage output and configured to:
operate based on an ET target voltage and a bias current to generate an ET modulated voltage at the voltage output for amplifying a radio frequency (RF) signal; and
cause an alternating current to flow through the voltage output in response to the RF signal being modulated above a defined modulation bandwidth; and
a bias modulation circuit configured to:
determine whether a level of the alternating current is between an upper current threshold and a lower current threshold lower than the upper current threshold, wherein the upper current threshold and the lower current threshold are configured to indicate whether the alternating current is approaching a defined current cross over point in between the upper current threshold and the lower current threshold; and
increase the bias current in response to the level of the alternating current being between the upper current threshold and the lower current threshold.
2. The ET voltage tracker circuit of claim 1 wherein the amplifier circuitry is further configured to:
receive the ET target voltage having a time-variant target voltage envelope; and
generate the ET modulated voltage having a time-variant voltage envelope tracking the time-variant target voltage envelope.
3. The ET voltage tracker circuit of claim 2 wherein the bias modulation circuit is further configured to increase the bias current to reduce a deviation between the ET modulated voltage and the ET target voltage.
4. The ET voltage tracker circuit of claim 2 wherein the bias modulation circuit is further configured to determine whether the level of the alternating current is between the upper current threshold and the lower current threshold based on the time-variant target voltage envelope of the ET target voltage.
5. The ET voltage tracker circuit of claim 1 wherein the bias modulation circuit is further configured to decrease the bias current in response to the level of the alternating current being outside the upper current threshold and the lower current threshold.
6. The ET voltage tracker circuit of claim 1 wherein the amplifier circuitry is preconfigured to operate based on an ideal level of the bias current.
7. The ET voltage tracker circuit of claim 6 wherein the bias modulation circuit is further configured to increase the bias current above the ideal level of the bias current in response to the level of the alternating current being lower than or equal to the upper current threshold and higher than or equal to the lower current threshold.
8. The ET voltage tracker circuit of claim 7 wherein the bias modulation circuit is further configured to decrease the bias current to the ideal level of the bias current in response to the level of the alternating current being higher than the upper current threshold or lower than the lower current threshold.
9. The ET voltage tracker circuit of claim 1 wherein the amplifier circuitry is further configured to generate a sense current indicative of the level of the alternating current caused by the amplifier circuitry at the voltage output.
10. The ET voltage tracker circuit of claim 9 wherein the sense current is proportionally related to the level of the alternating current flowing through the voltage output.
11. The ET voltage tracker circuit of claim 9 wherein the amplifier circuitry is further configured to:
generate the sense current as a positive sense current in response to the amplifier circuitry sourcing the alternating current; and
generate the sense current as a negative sense current in response to the amplifier circuitry sinking the alternating current.
12. The ET voltage tracker circuit of claim 9 wherein the bias modulation circuit is further configured to determine whether the level of the alternating current is between the upper current threshold and the lower current threshold based on the sense current.
13. The ET voltage tracker circuit of claim 9 further comprising a tracker output coupled to the voltage output of the amplifier circuitry via an offset capacitor, wherein the offset capacitor is configured to raise the ET modulated voltage to an ET modulated output voltage and provide the ET modulated voltage to the tracker output.
14. The ET voltage tracker circuit of claim 13 further comprising:
a multilevel charge pump configured to generate a direct-current-to-direct-current (DC-DC) voltage; and
an inductor coupled between the multilevel charge pump and the tracker output, the inductor configured to induce a direct current at the tracker output based on the DC-DC voltage.
15. The ET voltage tracker circuit of claim 1 wherein the upper current threshold is greater than 0 mA and the lower current threshold is smaller than 0 mA.
16. An envelope tracking (ET) power management circuit comprising a plurality of ET voltage tracker circuits, each of the plurality of ET voltage tracker circuits comprising:
amplifier circuitry comprising a voltage output and configured to:
operate based on a ET target voltage and a bias current to generate an ET modulated voltage at the voltage output for amplifying a radio frequency (RF) signal; and
cause an alternating current to flow through the voltage output in response to the RF signal being modulated above a defined modulation bandwidth; and
a bias modulation circuit configured to:
determine whether a level of the alternating current is between an upper current threshold and a lower current threshold lower than the upper current threshold, wherein the upper current threshold and the lower current threshold are configured to indicate whether the alternating current is approaching a defined current cross over point in between the upper current threshold and the lower current threshold; and
increase the bias current in response to the level of the alternating current being between the upper current threshold and the lower current threshold.
17. The ET power management circuit of claim 16 wherein the amplifier circuitry is further configured to generate a sense current indicative of the level of the alternating current caused by the amplifier circuitry at the voltage output.
18. The ET power management circuit of claim 17 wherein each of the plurality of ET voltage tracker circuits further comprises a tracker output coupled to the voltage output of the amplifier circuitry via an offset capacitor, wherein the offset capacitor is configured to raise the ET modulated voltage to an ET modulated output voltage and provide the ET modulated output voltage to the tracker output.
19. The ET power management circuit of claim 18 wherein each of the plurality of ET voltage tracker circuits further comprises:
a multilevel charge pump configured to generate a direct-current-to-direct-current (DC-DC) voltage; and
an inductor coupled between the multilevel charge pump and the tracker output, the inductor configured to induce a direct current at the tracker output based on the DC-DC voltage.
20. The ET power management circuit of claim 19 further comprising an amplifier circuit coupled to the tracker output and configured to amplify the radio frequency (RF) signal based on the ET modulated output voltage and the direct current.