The National Semiconductor LMV225 is a linear RF power meter IC in an SMD package. It can be used over the frequency range of 450 MHz to 2000 MHz and requires only four external components. The input coupling capacitor isolates the DC voltage of the IC from the input signal. The 10-k? resistor enables or disables the IC according to the DC voltage present at the input pin. If it is higher than 1.8 V, the detector is enabled and draws a current of around 5–8 mA. If the voltage on pin A1 is less than 0.8 V, the IC enters the shutdown mode and draws a current of only a few microampères. The LMV225 can be switched between the active and shutdown states using a logic-level signal if the signal is connected to the signal via the 10-kR resistor.

Circuit diagram:

 Linear RF Power Meter Circuit Diagram

 

The supply voltage, which can lie between +2.7 V und +5.5 V, is filtered by a 100nF capacitor that diverts residual RF signals to ground. Finally, there is an output capacitor that forms a low-pass filter in combination with the internal circuitry of the LMV225. If this capacitor has a value of 1 nF, the corner frequency of this low-pass filter is approximately 8 kHz. The corner frequency can be calculated using the formula fc = 1 ÷ (2 p COUT Ro) where Ro is the internal output impedance (19.8 k?). The output low-pass filter determines which AM modulation components are passed by the detector.

 

The output, which has a relatively high impedance, provides an output voltage that is proportional to the signal power, with a slope of 40 mV/dB. The output is 2.0 V at 9 dBm and 0.4 V at –40 dBm. A level of 0 dBm corresponds to a power of 1 mW in 50 R. For a sinusoidal wave-form, this is equivalent to an effective voltage of 224 mV. For modulated signals, the relationship between power and voltage is generally different. The table shows several examples of power levels and voltages for sinusoidal signals. The input impedance of the LMV225 detector is around 50 R to provide a good match to the characteristic impedance commonly used in RF circuits.

The data sheet for the LMV225 shows how the 40-dB measurement range can be shifted to a higher power level using a series input resistor. The LMV225 was originally designed for use in mobile telephones, so it comes in a tiny SMD package with dimensions of only around 1 × 1 mm with four solder bumps (similar to a ball-grid array package). The connections are labelled A1, A2, B1 and B1, like the elements of a matrix. The corner next to A1 is bevelled.

 

 

 

http://streampowers.blogspot.com/2012/06/linear-rf-power-meter-circuit.html 

Description

Here is a simple and humble 2 Watts mini audio amplifier circuit suitable for small pocket radios and other portable audio gadgets.The circuit is based on Phillips Semiconductors IC TDA 7052.The amplifier can be run even from a 3V Mercury button cell.This makes it ideal for battery operated gadgets.

The IC TDA7052 is a mono output amplifier coming in a 8-lead DI package (DIP). The device is mainly designed for battery-operated portable audio circuits. The features of TDA 7052 include ,no external components needed,  no switch-on or switch-off click sounds , great overall stability ,very low power consumption(quiescent current 4mA) , low THD, no  heat sinks required and short-circuit proof.

The gain of TDA 7052 is fixed internally at 40 dB. . To compensate the reduction of output power due to low voltage supply  the TDA7052 uses the Bridge-Tied-Load principle (BTL) which can provide  an output  of around 1 to 2 W  Rms(THD = 10%) into an 8 Ohm load with a power supply of 6 V.

In the circuit the potentiometer can be used to control the volume. Capacitor C1 and C2 are meant for  filtering the supply voltage if a battery eliminator is used as supply source. For operations using a battery C1 and C2 are not necessary.

Mini Audio Amplifier Circuit Diagram with Parts List:

Notes.

• Assemble the circuit on a good quality PCB or common board .
• If you are a little expert, you can assemble the  circuit in a match box including the speaker.