Technique for tuner automatic gain control circuit for mobile television applications
View Patent ↗A technique for providing stable tracking performance to an AGC loop circuit comprises amplifying a wideband radio frequency signal; detecting signals and blockers adjacent to the radio frequency signal; lowering a gain of the radio frequency signal; mixing a local oscillator signal with the radio frequency signal; shifting a frequency of the radio frequency signal from a radio frequency to an intermediate frequency; continuously varying a gain of the intermediate frequency signal; converting the intermediate frequency signal into a digital output signal; comparing the digital output signal with predefined thresholds comprising an upper threshold and a lower threshold; switching a post mixer amplifier (PMA) to a high gain state when an input of a variable gain amplifier (VGA) is greater than the upper threshold, and switching the PMA to a low gain state when an input of the VGA is lower than the lower threshold.
1. An automatic gain control (AGC) loop circuit comprising:
a low noise amplifier (LNA) that amplifies a wideband radio frequency signal;
a received signal strength indication (RSSI) unit that detects signals and blockers adjacent to said radio frequency signal, wherein said RSSI unit is coupled to said LNA;
a radio frequency AGC control unit that lowers a gain of said radio frequency signal;
a mixer that mixes a local oscillator (LO) signal with said radio frequency signal;
a bandpass filter that filters additional signal blockers adjacent to said radio frequency signal received from said mixer;
a post mixer amplifier (PMA) that amplifies an input signal of said PMA, wherein said PMA comprises a high gain state and low gain state;
a variable gain amplifier (VGA) that continuously varies a gain of an intermediate frequency signal;
an analog-to-digital converter (ADC) that converts said intermediate frequency signal into a digital output signal; and
an intermediate frequency AGC control unit that feeds said digital output signal to said PMA and compares said digital output signal with predefined thresholds comprising an upper threshold and a lower threshold,
wherein said PMA is switched to said high gain state when an input of said VGA is greater than said upper threshold, and
wherein said PMA is switched to said low gain state when an input of said VGA is lower than said lower threshold.
2. The AGC loop circuit of claim 1 , wherein said RSSI process unit down samples and performs signal processing of said radio frequency signal output from said LNA.
3. The AGC loop circuit of claim 1 , further comprising a radio frequency AGC control loop comprising said LNA, said RSSI unit, and said radio frequency AGC control unit.
4. The AGC loop circuit of claim 1 , further comprising an intermediate frequency AGC control loop comprising said bandpass filter, said PMA, said VGA, said ADC, and said intermediate frequency AGC control unit.
5. The AGC loop circuit of claim 3 , wherein said radio frequency AGC control loop comprises a bandwidth of approximately 10 Hz.
6. The AGC loop circuit of claim 4 , wherein said intermediate frequency AGC control loop comprises a bandwidth of approximately 400 Hz.
7. The AGC loop circuit of claim 5 , wherein said bandwidth of said radio frequency AGC control loop is programmable to obtain a tracking performance of said AGC loop circuit.
8. The AGC loop circuit of claim 6 , wherein said bandwidth of said intermediate frequency AGC control loop is programmable to obtain a tracking performance of said AGC loop circuit.
9. The AGC loop circuit of claim 1 , wherein said radio frequency AGC control unit strengthens an output signal of said RSSI process unit, and wherein said RSSI process unit reduces compression in said radio frequency signal output from said LNA.
10. A mobile television (TV) receiver comprising an automatic gain controller (AGC), wherein said AGC comprises:
a radio frequency (RF) AGC control loop comprising:
a low noise amplifier (LNA) that amplifies a wideband radio frequency signal;
a received signal strength indication (RSSI) unit that detects signals and blockers adjacent to said radio frequency signal, wherein said RSSI unit is coupled to said LNA; and
a RF AGC control unit that lowers a gain of said radio frequency signal;
a mixer that mixes a local oscillator (LO) signal with said radio frequency signal; and
an intermediate frequency (IF) AGC control loop comprising:
a bandpass filter that filters additional signal blockers adjacent to said radio frequency signal received from said mixer;
a post mixer amplifier (PMA) that amplifies an input signal of said PMA, wherein said PMA comprises a high gain state and low gain state;
a variable gain amplifier (VGA) that continuously varies a gain of an intermediate frequency signal;
an analog-to-digital converter (ADC) that converts said intermediate frequency signal into a digital output signal; and
an IF AGC control unit that feeds said digital output signal to said PMA and compares said digital output signal with predefined thresholds comprising an upper threshold and a lower threshold,
wherein said PMA is switched to said high gain state when an input of said VGA is greater than said upper threshold, and
wherein said PMA is switched to said low gain state when an input of said VGA is lower than said lower threshold.
11. The receiver of claim 10 , wherein said RSSI process unit down samples and performs signal processing of said output signal of said LNA.
12. The receiver of claim 10 , wherein said RF AGC control loop comprises a bandwidth of approximately 10 Hz.
13. The receiver of claim 10 , wherein said IF AGC control loop comprises a bandwidth of approximately 400 Hz.
14. The receiver of claim 10 , wherein said RF AGC control unit strengthens an output signal of said RSSI process unit, and wherein said RSSI process unit reduces compression in said output amplified signal of said LNA.
15. A method of providing stable tracking performance to an automatic gain control (AGC) loop circuit, said AGC loop circuit comprising (i) a radio frequency AGC control loop having a low noise amplifier (LNA) and a received signal strength indication (RSSI), and (ii) an intermediate frequency AGC control loop comprising a bandpass filter, a post mixer amplifier (PMA), and a variable gain amplifier (VGA), said method comprising:
amplifying a wideband radio frequency signal;
detecting signals and blockers adjacent to said radio frequency signal;
lowering a gain of said radio frequency signal;
mixing a local oscillator (LO) signal with said radio frequency signal;
shifting a frequency of said radio frequency signal from a radio frequency to an intermediate frequency;
continuously varying a gain of said intermediate frequency signal;
converting said intermediate frequency signal into a digital output signal;
comparing said digital output signal with predefined thresholds comprising an upper threshold and a lower threshold;
switching said PMA to a high gain state when an input of said VGA is greater than said upper threshold; and
switching said PMA to a low gain state when an input of said VGA is lower than said lower threshold.
16. The method of claim 15 , further comprising:
down sampling said radio frequency output from said LNA; and
performing signal processing of said radio frequency signal output from said LNA.
17. The method of claim 15 , wherein said radio frequency AGC control loop comprises a bandwidth of approximately 10 Hz.
18. The method of claim 15 , wherein said intermediate frequency AGC control loop comprises a bandwidth of approximately 400 Hz.
19. The method of claim 17 , wherein said bandwidth of said radio frequency AGC control loop is programmable to obtain a tracking performance of said AGC loop circuit.
20. The method of claim 15 , wherein said bandwidth of said intermediate frequency AGC control loop is programmable to obtain a tracking performance of said AGC loop circuit.