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OPTIMIZED FEEDBACK CONTROL CIRCUIT

IP.com Disclosure Number: IPCOM000241808D
Publication Date: 2015-Jun-02
Document File: 7 page(s) / 254K

Publishing Venue

The IP.com Prior Art Database

Abstract

This disclosure provides an optimized feedback control circuit to sustain variable load in a radio frequency power amplifier (RFPA). A coupler is added on a hybrid port 2 to couple the reflected power from a body coil. The gain of the transmitter chain remains unchanged irrespective of load variations. The optimized feedback control circuit derives a precise value of the specific absorption rate (SAR).

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OPTIMIZED FEEDBACK CONTROL CIRCUIT

BACKGROUND

The present invention relates generally to power amplifiers, and more particularly to an optimized feedback control circuit to sustain a variable load in a radio frequency power amplifier (RFPA).

There exist various conventional circuits that compensate amplitude and phase in a power amplifier.  However, during load variation, the conventional circuits are unable to efficiently control various parameters, such as compensation, gain and phase among others.  For example, there are compensation issues and further the gain and phase is found to be out of the specification during the load variation. 

Further, the conventional circuits need to perform an auto-pre-scan process for calculating a total gain (TG).  Furthermore, the conventional circuits are unable to calculate a precise value of specific absorption rate (SAR).

It would be desirable to have an optimized feedback control circuit to sustain the variable load in the radio frequency power amplifier (RFPA).  

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a graph showing gain variation according to a conventional compensation technique.

Figure 2 depicts a direction coupler.

Figure 3 depicts a conventional feedback control circuit.

Figure 4 depicts an optimized feedback control circuit according to the present invention.

Figure 5 depicts an optimized feedback control circuit having a coupler at port 2 according to the present invention.

DETAILED DESCRIPTION

This disclosure proposes an optimized feedback control circuit to sustain variable load in a radio frequency power amplifier (RFPA).  

Figure 1 is a graph showing a gain variation according to a conventional compensation technique.  A gain variation of about 0.6 dB is achieved under a load change condition.  

Figure 1

Figure 2 depicts a direction coupler.  The power on a load is P1 (Pi) – P2 (Pr).  If the load remains unchanged, the scale of a forward power (P1 FWD) with a reflected power (P2 REL) remains same, as S11 is unchanged.  Alternatively, if the load changes, the scale of the forward power (P1 FWD) with the reflected power (P2 REL) also changes.  The latter condition destroys a closed loop control and further makes the gain and phase out of specification.

Figure 2

Figure 3 depicts a conventional feedback control circuit.

Figure 3

Figure 4 depicts an optimized feedback control circuit according to the present invention.

The primary difference between the conventional feedback control circuit (shown in Fig 3) and the proposed optimized feedback control circuit (shown in Fig. 4) is that the conventional feedback circuit (Figure 3) uses a forward signal, while the optimized feedback circuit (Figure 4) uses a signal (FWD – RFL) for compensating the gain and phase.

Figure 4

Referring to Figure 2, the direction coupler is a bi-directional coupler having a coupling factor C and an isolation factor D.  

For easy understanding, let us assume that D is very larger than C, i.e. D >>C....