Radio-frequency amplifier system
View Patent ↗A device for measuring voltage levels includes a root mean square (RMS) detector. The RMS detector includes a linear multiplier, a log converter, a low-pass filter and a temperature compensator. The linear multiplier multiplies a voltage of an input signal by the voltage of the input signal. The low-pass filter couples to an output of the linear multiplier. The log converter generates a logarithmic signal having a voltage that is logarithmically related to a voltage of an output of the low-pass filter. The temperature compensator adjusts the logarithmic signal based on a temperature of the RMS detector. The RMS detector is capable of determine an RMS voltage level of the input signal.
1. A signal amplifier circuit, comprising:
an amplitude-modulated (AM) amplifier, operable to amplify an input AM signal, the AM amplifier comprising:
a first stage comprising a high-impedance input terminal operable to receive the input AM signal;
a second stage coupled to the first stage and operable to provide a gain of greater than one to an output of the first stage; and
a third stage coupled to the second stage, the third stage comprising a low-impedance output terminal operable to output an amplified AM signal;
a frequency-modulated (FM) amplifier operable to amplify an input FM signal, wherein the FM amplifier comprises a plurality of feedback paths and wherein an input impedance and an output impedance of the FM amplifier are substantially constant as a frequency of the input FM signal varies;
an automatic gain control (AGC) circuit comprising:
a first root-mean square (RMS) detector operable to measure an RMS voltage level of an input signal received by the AGC circuit; and
a first level adjuster, operable to adjust a voltage level of the input signal received by the AGC circuit based on the RMS voltage level measured by the first RMS detector; wherein the AGC circuit is operable to receive as the input signal an output signal of at least one of the AM amplifier and the FM amplifier and adjust the voltage level of that output signal;
a voltage supply operable to draw current from a source and to output a substantially stable voltage level at an output terminal;
wherein the AM amplifier, the FM amplifier, and the AGC circuit are coupled to the output terminal of the voltage supply.
2. The signal amplifier circuit of claim 1 wherein the signal amplifier circuit comprises a single integrated circuit package.
3. The signal amplifier circuit of claim 1 , wherein the high-impedance input terminal of the AM amplifier has an input impedance of greater than or equal to 1 mega-ohm.
4. The signal amplifier circuit of claim 1 , wherein the high-impedance input terminal of the AM amplifier has an input impedance sufficient to avoid loading the input AM signal.
5. The signal amplifier circuit of claim 1 , wherein the first stage of the AM amplifier comprises a metal-oxide semiconductor transistor.
6. The signal amplifier circuit of claim 1 , wherein the low-impedance output terminal of the third stage of the AM amplifier has an output impedance of less than or equal to 5 ohms.
7. The signal amplifier circuit of claim 6 , wherein the plurality of non-energetic negative feedback paths comprise an inductive series feedback path and a capacitive shunt feedback path.
8. The signal amplifier circuit of claim 7 , wherein the first level adjuster comprises an operational amplifier and the second level adjuster comprises an operational amplifier.
9. The signal amplifier circuit of claim 1 , wherein the FM amplifier comprises a plurality of non-energetic negative feedback paths.
10. The signal amplifier circuit of claim 1 , wherein:
the first level adjuster is further operable to adjust the voltage level of the output of the AM amplifier so that the voltage level of the output of the AM amplifier is within a predetermined voltage range; and
the second level adjuster is further operable to adjust the voltage level of the output of the FM amplifier so that the voltage level of the output of the FM amplifier is within a predetermined voltage range.
11. The signal amplifier circuit of claim 1 , wherein the first AGC circuit receives an output signal of the AM amplifier as the input signal of the first AGC circuit, and further comprising a second AGC circuit operable to receive an output signal of the FM amplifier as an input signal and comprising:
a second root-mean square (RMS) detector operable to measure a root-mean-square voltage level of the output signal of the FM amplifier; and
a second level adjuster, operable to adjust a voltage level of the output signal of the FM amplifier based on the voltage level measured by the second RMS detector; and
wherein the second AGC circuit is coupled to the output terminal of the voltage supply.