Voltage ripple suppression in a transmission circuit
Voltage ripple suppression in a transmission circuit is disclosed. The transmission circuit includes a power amplifier circuit coupled to an envelope tracking integrated circuit (ETIC) via a conductive path. Notably, the ETIC and the conductive path can present a large source impedance to the power amplifier circuit, which can cause a ripple in the modulated voltage received by the power amplifier circuit. In a conventional approach, the large source impedance may be isolated by a large decoupling capacitor at the expense of increased voltage switching time and battery current drain. In contrast, the ETIC disclosed herein can determine and apply a correction term to the modulated voltage generated by the ETIC to thereby suppress the ripple without requiring the large decoupling capacitor. By eliminating the large decoupling capacitor, the transmission circuit can thus achieve fast voltage switching with lower battery current drain.
1. A transmission circuit comprising:
a power amplifier (PA) circuit configured to amplify a radio frequency (RF) signal based on a modulated voltage received at a PA input; and
an envelope tracking (ET) integrated circuit (ETIC) comprising:
an ETIC output coupled to the PA input via a conductive path;
a voltage modulation circuit configured to generate the modulated voltage at the ETIC output based on a modulated target voltage and a feedback signal that indicates a selected one of the modulated voltage at the ETIC output and the modulated voltage at the PA input; and
a control circuit configured to:
generate a correction term based on the modulated voltage at the ETIC output and the modulated voltage at the PA input; and
apply the correction term to a selected one of the modulated target voltage and the feedback signal to cause the voltage modulation circuit to modify the modulated voltage to thereby suppress a ripple in the modulated voltage at the PA input.
2. The transmission circuit of claim 1 , wherein the voltage modulation circuit comprises:
a voltage amplifier comprising a positive input configured to receive the modulated target voltage and a negative input configured to receive the feedback signal, the voltage amplifier is configured to generate an initial modulated voltage based on the modulated target voltage and the feedback signal; and
an offset capacitor coupled between the voltage amplifier and the ETIC output, the offset capacitor is configured to raise the initial modulated voltage by an offset voltage to thereby generate the modulated voltage at the ETIC output.
3. The transmission circuit of claim 1 , further comprising a feedback circuit coupled between the ETIC output and the voltage modulation circuit and configured to generate the feedback signal that indicates the modulated voltage at the ETIC output.
4. The transmission circuit of claim 3 , wherein the control circuit is further configured to apply the correction term to the feedback signal to thereby cause the voltage modulation circuit to modify the modulated voltage.
5. The transmission circuit of claim 4 , wherein the correction term is a voltage correction term expressed as: −K*ΔV, wherein:
ΔV represents a voltage differential between the modulated voltage at the ETIC output and the modulated voltage at the PA input; and
K represents a gain factor.
6. The transmission circuit of claim 4 , further comprising an input circuit coupled between the control circuit and the voltage modulation circuit, the input circuit is configured to receive the correction term from the control circuit and apply the correction term to the feedback signal.
7. The transmission circuit of claim 6 , wherein the input circuit is configured to provide a time advance in the correction term.
8. The transmission circuit of claim 4 , wherein the correction term is a current correction term expressed as: −G m *ΔV, wherein:
ΔV represents a voltage differential between the modulated voltage at the ETIC output and the modulated voltage at the PA input; and
G m represents a transconductance that converts the voltage differential into the current correction term.
9. The transmission circuit of claim 8 , further comprising an input circuit coupled between the voltage modulation circuit and a ground, the input circuit is configured to convert the current correction term to a voltage correction term.
10. The transmission circuit of claim 3 , wherein the control circuit is further configured to apply the correction term to the modulated target voltage to thereby cause the voltage modulation circuit to modify the modulated voltage.
11. The transmission circuit of claim 10 , wherein the correction term is a current correction term expressed as: G m *ΔV, wherein:
ΔV represents a voltage differential between the modulated voltage at the ETIC output and the modulated voltage at the PA input; and
G m represents a transconductance that converts the voltage differential into the current correction term.
12. The transmission circuit of claim 11 , further comprising a target voltage circuit configured to:
receive the modulated target voltage;
receive the current correction term from the control circuit; and
modify the modulated target voltage based on the current correction term to thereby cause the voltage modulation circuit to modify the modulated voltage.
13. The transmission circuit of claim 11 , further comprising a resistor circuit configured to convert the current correction term into a voltage correction term.
14. The transmission circuit of claim 1 , further comprising a feedback circuit coupled between the PA input and the voltage modulation circuit and configured to generate the feedback signal that indicates the modulated voltage at the PA input.
15. The transmission circuit of claim 14 , wherein the control circuit is further configured to apply the correction term to the feedback signal to thereby cause the voltage modulation circuit to modify the modulated voltage.
16. The transmission circuit of claim 15 , wherein the correction term is a voltage correction term expressed as: −K*ΔV, wherein:
ΔV represents a voltage differential between the modulated voltage at the ETIC output and the modulated voltage at the PA input; and
K represents a gain factor.
17. The transmission circuit of claim 15 , further comprising an input circuit coupled between the control circuit and the voltage modulation circuit, the input circuit is configured to receive the correction term from the control circuit and apply the correction term to the feedback signal.
18. The transmission circuit of claim 17 , wherein the input circuit is configured to provide a time advance in the correction term.
19. The transmission circuit of claim 1 , wherein the control circuit comprises an operational amplifier (op-amp) having a negative op-amp input coupled the ETIC output and a positive op-amp input coupled to the PA input, the op-amp is configured to generate the correction term based on a voltage differential between the modulated voltage at the ETIC output and the modulated voltage at the PA input.
20. The transmission circuit of claim 19 , wherein the control circuit further comprises a compensation circuit coupled between the negative op-amp input and the positive op-amp input, the compensation circuit is configured to generate a compensation term in the correction term to thereby offset a variation in the voltage differential resulting from a decoupling capacitor coupled to the PA input and a ground.