专利汇可以提供Power control circuit for radio frequency power amplifiers专利检索,专利查询,专利分析的服务。并且A power control circuit for regulating an output voltage applied to a radio frequency power amplifier. The power control circuit includes an amplifier, a pass transistor and one or more saturation detectors. An input ramp voltage having a magnitude equal to a first voltage level is applied to a negative terminal of the amplifier. The pass transistor provides an output voltage at a drain terminal of the pass transistor. The saturation detector detects a magnitude of a voltage at a gate terminal of the pass transistor and generates a control current based on the magnitude of the voltage at the gate terminal of the pass transistor. The voltage regulating circuit reduces the magnitude of the input ramp voltage from the first voltage level to a third voltage level based on the control current.,下面是Power control circuit for radio frequency power amplifiers专利的具体信息内容。
What is claimed is:
The present invention generally relates to the field of radio frequency (RF) power amplifiers. More specifically, it relates to Complementary Metal Oxide Semiconductor (CMOS) power control circuits used in the Global System for Mobile (GSM) communication power amplifier modules.
GSM is a digital mobile telephony system used for cellular communication. The GSM technology uses Gaussian Minimum Shift Keying (GMSK) which is a continuous-phase frequency-shift keying (FSK) modulation. GMSK entails passing a modulating signal through a Gaussian filter, subsequent to which a carrier signal is modulated using the filtered modulating signal. Modulating the carrier signal includes varying the frequency of the carrier signal at carrier zero crossing points such that the GMSK modulated carrier signal has a continuous phase and a constant amplitude envelope.
RF power amplifiers which include non-linear power amplifiers are used to amplify the GMSK modulated carrier signal. The amplification provided by such RF power amplifiers is proportional to the amplitude of an input signal. This results in a distorted output signal in a scenario when the amplitude of the input signal varies. Thus, the constant amplitude envelope of the GMSK modulated signals renders such signals immune to distortion due to non-linear amplification. Therefore, RF amplifiers may be used for power control of GMSK modulated signals without distorting the signals. Additionally, the constant amplitude envelope of the GMSK modulated signals permits the RF power amplifiers to operate near saturation, which in turn results in energy efficiency. The energy efficient operation of the RF amplifiers enables reduction in the size of mobile hand set and minimization of the power consumption to conserve life of the battery used in the mobile handset.
The RF output signal is composed of multiple signals having different frequencies spread over a frequency spectrum. In accordance with European Telecommunication Standard Institute (ETSI) specifications, the frequency band of the RF output signal should be limited to a predefined frequency range or have a predefined switching spectrum. The frequency range of the RF output signal spectrum depends upon the operation of the RF power amplifier which in turn is governed by a biasing voltage. Thus, to limit the RF output signal spectrum to a predefined range, a power control circuit is used to control the biasing voltage provided to the RF power amplifier. The operation of the power control circuit is explained below in conjunction with
An output terminal of amplifier 106 is coupled to a gate terminal of pass transistor 108. A source terminal of pass transistor 108 is coupled to voltage source 110. Voltage source 110 provides a voltage (Vbat) to the source terminal of pass transistor 108 having a maximum magnitude equal to a second voltage level when voltage source 110 is completely charged. A drain terminal of pass transistor 108 is coupled to RF power amplifier block 102. Further, an output voltage (Vout) is obtained at the drain terminal of pass transistor 108. Vout is provided as biasing voltage to the one or more power amplifiers of RF power amplifier block 102.
Power control circuit 104 includes resistor R1 through which Vout is fed back as a feedback voltage to a positive terminal of amplifier 106. A first end of resistor R1 is connected to the drain terminal of pass transistor 108. A second end of resistor R1 is connected to the positive terminal of amplifier 106 and a first end of resistor R2. A second end of resistor R2 is coupled to a first end of resistor R3 and a first end of resistor R4. A second end of resistor R4 is connected to ground.
RF power amplifier block 102 amplifies an input RF signal to produce an output RF signal in which the power of the output RF signal is controlled by RF power amplifier block 102. Power control circuit 104 controls the biasing voltage Vout which is provided to the one or more power amplifiers of RF power amplifier block 102. The control of the biasing voltage Vout in turn controls the power of the output RF signal. Further, power control circuit 104 operates as a low drop-out voltage regulator (LDO). The operation of the LDO is based on a feedback loop, which includes feeding back Vout to the positive terminal of amplifier 106. Amplifier 106 provides an amplified error voltage at the output terminal by amplifying a difference between the feedback voltage applied at the positive terminal of amplifier 106 and Vramp applied at the negative terminal of amplifier 106. The amplified error voltage is applied to the gate terminal of pass transistor 108 and has a magnitude equal to Vgpass. The feedback voltage depends on Vout and is equal to a voltage at the second end of resistor R1. Vout depends on the amplified error voltage. For a predefined profile and magnitude of Vramp applied at the negative terminal of amplifier 106, power control circuit 104 regulates Vout at the drain terminal of pass transistor 108. As a result of which power at the output of RF amplifier block 102 is controlled.
Power at the output of RF amplifier block 102 is constant under normal operating conditions for an applied voltage Vramp during which the magnitude of Vout is sufficiently lower than Vbat. However, as voltage source 110 discharges, Vbat reduces below the maximum magnitude, i.e., the second voltage level, and drops below the Vout voltage levels for high power settings. The gain in the error amplifier 106 then decreases since Vout exceeds Vbat. Also, the voltage drop between Vbat and Vout decreases, causing pass transistor 108 to operate in the triode region. As a result, the unity gain frequency and loop gain of power control circuit 104 degrades and hence the transfer function characteristics of power control circuit 104 become distorted. As a consequence, Vout applied to RF power amplifier block 102 is distorted. In addition, Vgpass drops significantly due to the decrease in gain of amplifier 106. This introduces slewing transients and delay in the feedback loop of power control circuit 104 when more current is required to recharge parasitic capacitances at the gate terminal of pass transistor 108. Further, the reduced Vbat prevents Vout from reaching its maximum value, causing clipping of the ramp voltage profile at output of amplifier 106. As a result, spurious non linear components are introduced in the output of amplifier 106 which degrades Vout applied to RF power amplifier block 102.
Due to the reduction in Vbat, the slewing transients and delays are introduced in the feedback loop of power control circuit 104 and due to the variations in Vout, spurious frequency components are introduced in the frequency spectrum of the RF output signal. This degrades the RF output signal frequency spectrum and causes the RF output signal to violate the frequency requirements defined by the ETSI.
In light of the above, a need exists for a power control circuit that regulates an output voltage applied to RF power amplifier block. Further, a need exists for a power control circuit that prevents the transfer function characteristics of the power control circuit from becoming distorted, thereby maintaining the required switching spectrum when the magnitude of the voltage provided by the voltage source reduces. Still further, a need exists for a power control circuit that can reduce the effect of slewing due to large capacitance at the gate terminal of pass transistor and prevents the non-linear operation of amplifier, thereby preventing degradation of the switching spectrum. Furthermore, there is a need for a power control circuit that reduces clipping of the applied ramp voltage profile at reduced voltage level of the voltage source.
An object of the present invention is to provide a power control circuit that regulates the output voltage applied to a RF power amplifier block.
Another object of the present invention is to provide a power control circuit that maintains the desired switching spectrum at reduced voltage level of a voltage source.
Another object of the present invention is to provide a power control circuit that maintains the desired transfer function characteristics of the power control circuit.
Another object of the present invention is to provide a power control circuit that reduces the effect of slewing due to large capacitance at the gate terminal of pass transistor.
Yet another object of the present invention is to provide a power control circuit that reduces clipping of the applied ramp voltage profile at reduced voltage level of the voltage source.
Yet another object of the present invention is to provide a compact power control circuit.
Still another object of the present invention is to provide a power control circuit that optimizes peak efficiency of a RF power amplifier block.
Still another object of the present invention is to provide a power control circuit that minimizes added noise in receive band.
In accordance with the objects of the invention, various embodiments of the invention provide a power control circuit that regulates an output voltage applied to a RF power amplifier block. The power control circuit includes an amplifier, a pass transistor, at least one saturation detector, and a voltage regulating circuit. An input ramp voltage having a magnitude equal to a first voltage level is applied to a negative terminal of the amplifier. The pass transistor provides an output voltage at a drain terminal thereof which is fed back to a positive terminal of the amplifier. The voltage source provides a voltage having a magnitude equal to a second voltage level to a source terminal of the pass transistor. The saturation detector detects a magnitude of a voltage at a gate terminal of the pass transistor and generates a control current based on the magnitude of the voltage at the gate terminal of the pass transistor. The voltage regulating circuit reduces the magnitude of the input ramp voltage from the first voltage level to a third voltage level based on the control current.
In accordance with the objects of the invention, various embodiments of the invention provide a power control circuit for regulating an output voltage applied to a RF power amplifier block. At least one saturation detector detects a magnitude of a voltage at a gate terminal of a pass transistor and increases magnitude of a voltage at a positive terminal of an amplifier based on the magnitude of the voltage at the gate terminal of the pass transistor.
Various embodiments of the invention will hereinafter be described in conjunction with the appended drawings, provided. To illustrate and not to limit the invention, wherein like designations denote like elements, and in which:
Various embodiments of the invention provide a power control circuit for regulating an output voltage applied to a RF power amplifier block. The power control circuit maintains the required switching spectrum when the magnitude of voltage provided by a voltage source reduces. The power control circuit comprises a saturation detector and voltage regulating circuit which regulates input ramp voltage based on magnitude of voltage at a gate terminal of a pass transistor in the power control circuit.
Voltage regulating circuit 220 is coupled to a negative terminal of amplifier 206. An input ramp voltage (Vramp
Power control circuit 204 includes resistor R1 through which Vout is fed back as a feedback voltage to a positive terminal of amplifier 206. A first end of resistor R1 is connected to the drain terminal of pass transistor 208. A second end of resistor R1 is connected to the positive terminal of amplifier 206 and a first end of resistor R2. A second end of resistor R2 is coupled to a first end of resistor R3 and a first end of resistor R4. A second end of resistor R4 is connected to ground.
RF power amplifier block 202 amplifies an input RF signal RFin to produce an output RF signal RFout in which the power of the output RF signal is controlled by RF power amplifier block 202. Power control circuit 204 controls the biasing voltage Vout which is provided to the one or more power amplifiers of RF power amplifier block 202. The control of the biasing voltage Vout in turn controls the power of the output RF signal. Power control circuit 204 operates as a low drop-out voltage regulator (LDO). The operation of the LDO is based on a feedback loop, which includes feeding back Vout to the positive terminal of amplifier 206. Amplifier 206 provides an amplified error voltage at the output terminal by amplifying a difference between the feedback voltage applied at the positive terminal of amplifier 206 and Vramp
When Vbat reduces below the maximum magnitude, i.e., the second voltage level, due to discharge of voltage source 210, maximum value of Vout begins to saturate close to Vbat. As a result, the gain of error amplifier 206 decreases which causes Vgpass to decrease. At least one saturation detector 212 detects the magnitude of Vgpass. When the magnitude of Vgpass is reduced below a fourth voltage level, sense transistor 214 is switched on. In an embodiment of the present invention, the fourth voltage level is equal to a difference between a fifth voltage level and a threshold voltage. The threshold voltage level is equal to difference between the gate terminal voltage of sense transistor 214 and a voltage at a source terminal of sense transistor 214 at which sense transistor 214 is switched on.
When sense transistor 214 is switched on, a control current I1 flows from at least one saturation detector 212 to current mirror 216. This results in a current I2, which is proportional to I1, flowing from voltage regulating circuit 220 towards current mirror 216. Since, I2 flows through resistor R5, a voltage drop equal to I2R5 occurs across resistor R5. As a result, Vramp
Due to increase in Vgpass, VOut reduces and pass transistor 208 operates in the saturation region. Consequently, the loop gain and unity gain frequency increases and hence the desired transfer function characteristics of power control circuit 204 is obtained at the reduced Vbat. Further, slewing caused due to charging of the large parasitic capacitances at the gate terminal of pass transistor 208 is minimized since Vgpass does not reduce to a low value. Further, clipping of the ramp voltage profile is reduced when Vbat reduces since the maximum Vout voltage does not saturate. Thus, power control circuit 204 regulates Vout and maintains the required switching spectrum behavior when Vbat is reduced.
As explained above, a power control circuit 304 operates as a LDO which includes feeding back Vout to the positive terminal of amplifier 306 through resistor R1 as the feedback voltage. Further, amplifier 306 receives Vramp at the negative terminal of amplifier 306. Amplifier 306 provides an amplified error voltage by amplifying a difference between the feedback voltage applied at the positive terminal of amplifier 306 and Vramp applied at the negative terminal of amplifier 306. The amplified error voltage is applied to the gate terminal of a pass transistor 308 and to the gate terminal of a sense transistor 314. The amplified error voltage has a magnitude equal to Vgpass. Sense transistor 314 is configured to switch on when Vgpass decreases below the fourth voltage level. As explained in conjunction with
Various embodiments of the invention provide several advantages. The power control circuit maintains the switching spectrum behavior defined by the European Telecommunications Standard Institute (ETSI) at reduced voltage level of a voltage source. Further, the power control circuit is compact since it requires a small number of transistors and a small amount of layout space.
Further, the power control circuit optimizes peak efficiency of a RF power amplifier module under nominal conditions. The efficiency of the LDO is equal to ratio of Vbat and Vout. The peak power and efficiency of a power amplifier module increases when the maximum value of Vout becomes equal to Vbat. So, whereas this arrangement achieves proper switching spectrum behavior, it somewhat degrades the power amplifier module's power and efficiency since it decreases the maximum Vout. Under nominal conditions, when the magnitude of Vbat is equal to the second voltage level, the power control circuit does not limit Vout. When the magnitude of Vgpass is reduced below the fourth voltage level, the power control circuit decreases Vout and Vgpass proportionally to Vbat. As a result, peak power and efficiency of the power amplifier module remains unaffected by reduction in magnitude of Vbat.
Moreover, the power control circuit has a small number of circuit components that produce noise. As a result, the power control circuit minimizes added noise in the receive band as compared to more complex schemes that have additional components. Still further, the power control circuit reduces clipping of the applied ramp voltage profile at reduced voltage levels of the voltage source. Still further, the power control circuit reduces the effect of slewing caused due to charging of the large parasitic capacitances at the gate terminal of pass transistor
While various embodiments of the present invention have been illustrated and described, it will be clear that the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art, without departing from the basic scope and spirit of the invention, as described in the claims that follow.
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