TOI and power compression bias network

The present invention relates to a method and/or architecture for implementing active bias networks generally and, more particularly, an active bias network configured to increase Third-Order Intercept, the 1 dB (decibel) compression point, and improve noise performance of an integrated circuit (IC) amplifier. The present invention may also provide a simplified method of packaging.

Referring to FIG. 1, a typical amplifier 10 that may be used for biasing is shown. The amplifier 10 implements a resistor string RA and RB for biasing. The resistor string RA and RB provides a correct base (or gate voltage) for a desired device current. However, the resistor string (or divider) RA and RB does not provide temperature or process variation correction.

Referring to FIG. 2, a typical biased amplifier circuit is shown. The amplifier 20 includes a bias network of a number of resistors R 1 , R 2 , R 3 , R 4 , and R 5 , a transistor Q 1 , a transistor Q 2 and a capacitor C 1 . The amplifier 20 includes the bias network to provide temperature and process variation correction. However, the bias network does not correct for the non-linearity of the network.

The present invention concerns an apparatus comprising an amplifier and a circuit. The amplifier may be configured to amplify an input signal. The circuit may be configured to (i) control the amplifier, (ii) compensate for non-linear characteristics of the amplifier and (iii) increase the third-order intercept (TOI).

The objects, features and advantages of the present invention include providing a method and/or architecture for active bias networks that may (i) improve the third-order intercept (TOI) (ii) improve noise performance of an integrated circuit amplifier, (iii) improve the 1 dB compression point without the use of external components, (iv) implement a three terminal integrated circuit and/or (v) be implemented in a low cost package.

These and other objects, features and advantages of the present invention will be apparent from the following detailed description and the appended claims and drawings in which:

FIG. 1 is a schematic of a conventional amplifier biasing circuit;

FIG. 2 is a schematic of a conventional amplifier biasing circuit with temperature and process variation correction;

FIG. 3 is a schematic of a preferred embodiment of the present invention;

FIG. 4 is a schematic of another embodiment of the present invention;

FIG. 5 is a schematic of another embodiment of the present invention;

FIG. 6 is a schematic of another embodiment of the present invention;

FIG. 7 is a graph of a harmonic balance simulation illustrating an operation of the present invention; and

FIG. 8 is a graph of a DC simulation illustrating an operation of the present invention.

Referring to FIG. 3, a block diagram of a circuit (or system) 100 is shown in accordance with a preferred embodiment of the present invention. The circuit 100 may be implemented as an active bias network and integrated circuit (IC) amplifier. The circuit 100 generally comprises a block (or circuit) 102 and a block (or circuit) 104 . In one example, the circuit 102 may be implemented as an active bias network and the circuit 104 may be implemented as an IC amplifier. The active bias network 102 may be configured to control the amplifier 104 . The amplifier 104 may be configured to generate an amplified signal (not shown).

The active bias network 102 may be designed to increase the third-order intercept (TOI), the 1 dB compression point and/or improve the noise performance of the IC amplifier 104 . TOI may be the extrapolated power level, where the fundamental output power intercepts the extrapolated third-order intermodulation product output power level. The third-order intercept (TOI) point may be a measure of a power level where significant undesired non-linear distortion of a communication signal occurs. For example, the TOI may be related to a maximum signal that may be processed without causing significant problems to the accurate reproduction of desired information (e.g., a wireless telephone signal, or a TV signal).

The active bias network 102 may allow for low cost three terminal packages to be implemented. The circuit 100 may allow the active bias network 102 to provide improved RF performance. The circuit 100 may also allow the network 102 to implement tuning to compensation for non-linear characteristics of the active bias network 102 and further increase the TOI.

The circuit 102 may have an input 106 that may receive a power supply (e.g., VCC). The circuit 104 may have an input 108 that may receive the power supply VCC. The circuit 102 generally comprises a number of resistors (e.g., R 1 , R 2 , R 3 , R 4 and R 5 ), a capacitor (e.g., C 1 ), a capacitor (e.g., C 2 ), a device (e.g., Q 1 ), a device (e.g., Q 2 ), and an inductor (e.g., L 1 ). A resistance of the resistors R 1 -R 5 may be varied in order to meet the criteria of a particular implementation. A capacitance of the capacitors C 1 and C 2 may be varied in order to meet the criteria of a particular implementation. The devices Q 1 and Q 2 may be implemented as CMOS, NPN, PNP, MESFET, PHEMT, or MOSFET type devices. However, the particular type of the devices Q 1 and Q 2 may be varied in order to meet the criteria of a particular implementation. The inductance of inductor L 1 may also be varied in order to meet the criteria of a particular implementation.

The inductor L 1 and the capacitor C 2 may be configured to compensate for the non-linearity of the active bias network 102 . The active bias network 102 may be a non-linear device and may generate harmonics similar to the non-linearity of the main amplifier 104 . If the amplitude and the phase of the harmonics of the active bias network 102 are adjusted in proper relationship to the harmonics of the amplifier 104 , then cancellation of a portion of the non-linearity may occur. The inductor L 1 and the capacitor C 2 may also be configured to shunt current of the circuit 100 to modify the amplitude and phase of the harmonics of the active bias network 102 , such that the harmonics are partially canceled. Additionally, the inductor L 1 and the capacitor C 2 may be tuned to maximize the TOI and center performance in a particular frequency band of interest.

Referring to FIG. 4, a circuit 100 ′ illustrating another embodiment of the present invention is shown. The circuit 100 ′ may be similar to the circuit 100 . The circuit 100 ′ may implement an additional diode (e.g., D 1 ) and a capacitor (e.g., C 3 ) to provide increased point dB. The diode D 1 and the capacitor C 3 may be implemented to increase the TOI of the main amplifier 104 , to increase the 1 dB compression point, and eliminate the need for additional external tuning components (e.g., the inductor L 1 and the capacitor C 2 ). The diode D 1 may improve the phase and amplitude response of the amplifier 104 . However, the circuit 100 ′ may require an additional resistor string (e.g., R 6 ) to bias the amplifier 104 . The resistor network 100 of FIG. 3 does not generally provide temperature or process compensation. Therefore, the compensation diode D 1 and the compensation capacitor C 3 may be implemented within the active bias circuit 102 ′ to (i) provide both temperature and process compensation, (ii) increase the 1 dB compression point, and/or (iii) increase TOI.

Referring to FIG. 5, a circuit 100 ″ illustrating another embodiment of the present invention is shown. The circuit 100 ″ may be similar to the circuits 100 and 100 ′. The circuit 100 ″ may additionally implement an inductor (e.g., L 2 ) to reduce noise created by the circuit 102 ″ and/or the output signal from the amplifier 104 ″ that is being fed back to the circuit 102 ″. The active bias network 102 of FIG. 3 may add additional noise to the main amplifier 104 . Therefore, the active bias network 102 ″ may implement the inductor L 2 to increase the isolation of the active bias network 102 ″ from the main amplifier 104 ″ at RF frequencies and decrease the noise contribution from the active bias network 102 ″. However, the inductor L 2 may reduce the effectiveness of the linearity improvement of the active bias network 102 ″. The circuit 100 ″ may have a tradeoff between improved noise performance and improved linearity performance.

Referring to FIG. 6, a circuit 100 ′″ illustrating another embodiment of the present invention is shown. The circuit 100 ′″ may be similar to the circuits 100 , 100 ′ and 100 ″. The circuit 100 ″ may implement an additional inductor (e.g., L 3 ) and a capacitor (e.g., C 4 ) to further reduce noise. The circuit 100 ′″ may be implemented in a single three terminal package which may eliminate the need for expensive and/or larger RF and non-RF compatible multi-pin packages. Therefore, the IC amplifier 104 ′″ may be smaller and more user friendly, while reducing the amount of required external components. The improvements illustrated in the circuit 100 ′″ of FIG. 6 (e.g., the inductor L 3 and the capacitor C 4 ) may be implemented with any of the embodiments (e.g., the circuits 100 , 100 ′ or 100 ″) of the present invention.

Referring to FIG. 7, a graph 150 illustrating a harmonic balance simulation of the circuit 20 of FIG. 2 and the circuit 100 ′ of FIG. 4 is shown. The markers M 3 and M 4 illustrate the gain and 1 dB compression point for the circuit 100 ′. The marker M 5 may be the output power of the amplifier 104 ′ at the 1 dB compression point. The markers M 1 and M 2 may be the gain and 1 dB compression point for the circuit 20 . The marker M 6 may be the output power at the 1 dB compression point for the circuit 20 .

Referring to FIG. 8, a graph 200 illustrating a DC simulation of the circuit 20 of FIG. 2 and the circuit 100 ′ of FIG. 4 is shown. The graph 200 may illustrate a collector current (e.g., Ic) and a base-emitter voltage (e.g., Vbe) of the main amplifier 104 ′. The marker M 7 may be the current through the main amplifier of the circuit 20 at the 1 dB compression point. The marker M 8 may be the current through the amplifier 104 ′ of the circuit 100 ′ at the 1 dB compression point. The graph 200 may also illustrate that the Vbe of the circuit 100 ′ may remain fairly constant between the input power range of −10 dBm to +24 dBm. The graph 200 may illustrate that the Vbe of the circuit 20 is constant only over the input power range of −10 dBm to +5 dBm. Over the same −10 dBm to +24 dBm input power range Vbe, the circuit 20 may change more than 20%. The power added efficiency (PAE) of the circuit 20 may be 42.1% at the 1 dB compression point defined by the marker M 6 of the graph 150 of FIG. 7 . The PAE of the circuit 100 ′ of FIG. 4 may be 49.4% at the 1 dB compression point defined by the marker M 5 of the graph 200 of FIG. 7 .

The circuit 100 ′ of FIG. 4 may have a higher 1 dB compression point, (e.g., a 1.3 dB improvement over the circuit 20 ). The circuit 100 ′ may have a higher PAE (e.g., a 7.3% increase over the circuit 20 ). The circuit 100 ′ may also maintain a constant Vbe over a larger input power range. However, the circuit 100 ′ may have approximately 0.5 dB less gain. The simulations 150 and 200 may illustrate that the diode D 1 , the capacitor C 3 and the resistor string R 6 may improve the dB compression point by 1-1.5 dB.

The circuit 100 may implement the inductor L 1 and the capacitor C 2 to improve TOI. The circuit 100 may implement the diode D 1 and the capacitor C 3 to improve the 1 dB compression point without the use of external components. The circuit 100 may implement the inductor L 2 to improve noise performance of the amplifier 104 . The circuit 100 may implement the inductor L 3 and the capacitor C 4 to allow a three terminal integrated circuit to be provided in a low cost package.

The circuit 100 may implement the active bias network 102 to provide tuning to compensate for non-linear characteristics of the active bias network 102 and increase the third-order intercept point. The circuit 100 may also increase the point P1 dB of the main IC amplifier 104 and eliminate any additional external tuning components. Additionally, the circuit 100 may be implemented within a single low cost package.

The circuit 100 may be implemented within the wireless market to meet various high performance requirements for RF components. Specifically, the circuit 100 may provide an amplifier with high performance in the area of higher linearity, higher output power compression, and lower noise. The circuit 100 may also allow simultaneous use of an active bias network to provide temperature and process compensation, improve linearity, output power compression and noise performance. Additionally, the circuit 100 may be used in low noise amplifier and power amplifier applications.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.