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LMV242MDA データシート(PDF) 11 Page - National Semiconductor (TI) |
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LMV242MDA データシート(HTML) 11 Page - National Semiconductor (TI) |
11 / 16 page Application Section POWER CONTROL PRINCIPLES The LMV242 is a member of the power loop controller family of National Semiconductor, for quad-band TDMA/GSM solu- tions. The typical application diagram demonstrates a basic approach for implementing the quad-band solution around an RF Power Amplifier (PA). The LMV242 contains a 50 dB Logamp detector and interfaces directly with the directional coupler. The LMV242 Base Band (control-) interface consists of 3 signals: TX_EN to enable the device, BS to select either output 1 or output 2 and V RAMP to set the RF output power to the specified level. The LMV242 gives maximum flexibility to meet GSM frequency- and time mask criteria for many dif- ferent single supply Power Amplifier types like HBT or Mes- FET in GaAs, SiGe or Si technology. This is accomplished by the programmable Ramp characteristic from the Base Band and the TX_EN signal along with the external compensation capacitor. POWER AMPLIFIER CONTROLLED LOOP This section gives a general overview and understanding of how a typical Power Amplifier control loop works and how to solve the most common problems confronted in the design. General Overview The key benefit of a PA control loop circuit is its immunity to changes in the PA gain control function. When a PA control- ler is used, the relationship between gain and gain control voltage (V APC) of the PA is of no consequence to the overall transfer function. It is a function of the controller’s V RAMP voltage. Based upon the value of V RAMP, the PA controller will set the gain control voltage of the PA to a level that is necessary to produce the desired output level. Any tempera- ture dependency in the PA gain control function will be eliminated. Also, non-linearity’s in the gain transfer function of the PA do not appear in the overall transfer function (P OUT vs. V RAMP). The only requirement is that the gain control function of the PA has to be monotonic. To achieve this, it is crucial, that the LMV242’s detector is temperature stable. Typical PA Closed Loop Control Setup A typical setup of PA control loop is depicted in Figure 1. Beginning at the output of the Power Amplifier (PA), this signal is fed, usually via a directional coupler, to a detector. The error between the detector output current I DET and the ramp current I RAMP, representing the selected power setting, drives the inverting input of an op amp, configured as an integrator. A reference voltage drives the non-inverting input of the op amp. Finally the output of the integrator op amp drives the gain control input of the power amplifier, which sets the output power. The loop is stabilized when I DET is equal to I RAMP . Lets examine how this circuit works in detail. 20079528 FIGURE 1. PA Control Loop www.national.com 11 |
同様の部品番号 - LMV242MDA |
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同様の説明 - LMV242MDA |
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