TH35495A - Intermediate frequency (IF) system of the receiver with active filtering. - Google Patents

Abstract

DC60 (09/04/41) A high-range dynamic receiver IF system, employing a limiting dynamic range IF filter, is revealed. A variable-gain amplifier amplifies the first IF signal. This amplified first IF signal is fed to a shadow suppression combination circuit to suppress the shadow components of the amplified first IF signal, providing sufficient shadow suppression for the radio system. The shadow suppression combination circuit outputs a second shadow-suppressed IF signal. An active band-pass filter filters out unwanted components from the second IF signal. The filtered signal is then strictly limited in a limiting amplifier, which outputs a limited IF signal. A logarithmic detector is provided with a gain indicator. A high-range dynamic receiver IF system, employing a limiting dynamic range IF filter, is revealed. A variable-gain amplifier amplifies the first IF signal. This amplified first IF signal... The signal is fed to a shadow-suppressing combination circuit for suppression of the shadow components of the amplified first IF signal, providing sufficient shadow suppression for the radio system. The shadow-suppressing combination circuit then outputs a second shadow-suppressed IF signal. An active band-pass filter filters out unwanted components from the second IF signal. The filtered signal is then strictly limited in a limiting amplification circuit, which outputs a limited IF signal. A logarithmic detector is provided to determine the received signal strength.

Claims (17)

1. A high-dynamic-range receiver IF system employs a limited-dynamic-range IF filter circuit comprising: a variable-gain amplifier for amplifying the first IF signal; a shadow suppression combination for suppressing shadow components of the amplified first IF signal to provide sufficient shadow suppression for the radio system; this shadow suppression combination outputs a second shadow-suppressed IF signal; an active band-pass filter for filtering unwanted components from the second IF signal; a limiting amplifier for strictly limiting the filtered signal and outputting a limited IF signal; and a logarithmic detector for providing a signal strength indicator. 2. The receiver's IF system, compliant with claim 1, has a variable gain amplifier controlled by an automatic gain control circuit. 3. The receiver's IF system, compliant with claim 1, has a variable-gain amplifier circuit digitally controlled by a microcontroller. 4. The receiver's IF system, compliant with claim 1, contains a logarithmic detector and devices to eliminate the effects of gain variation so that the signal strength indicator is not degraded by the variable gain of a variable gain amplifier circuit. 5. The receiver's IF system, compliant with claim 1, further includes: a downtransform section for converting the second IF signal into a phase-matched and orthogonal baseband signal. 6. The receiver's IF system, in accordance with claim 1, shall also include: a conversion section for converting the second IF signal to another frequency. 7. The receiver's IF system, in accordance with claim 1, shall consist of: a voltage-controlled oscillator for providing a tunable frequency signal to the shadow suppression mixing circuit, which shall then mix this tunable frequency signal with the first IF signal in order to change the frequency of the first IF signal. 8. The receiver's IF system, in accordance with claim 1, shall consist of: a second active band-pass filter device centered around the second center frequency; a switching device for the selective coupling of the said first and second active band-pass filter devices; and such logarithmic detector. 9. A high-dynamic-range receiver IF system utilizing a limited-dynamic-range IF filter circuit comprising: a shadow suppression combination circuit for suppressing shadow components of the first IF signal to provide sufficient shadow suppression for the radio system; such shadow suppression combination circuit outputting the shadow-suppressed second IF signal; a variable-gain amplification circuit for amplifying the second IF signal; an active-band-pass filter (BATF) device for filtering unwanted components from the second IF signal; a limiting amplification device for strictly limiting the second IF signal and outputting a limited IF signal; and a logarithmic detector for providing a signal strength indicator derived from the filtered signal. 10. The receiver's IF system, compliant with claim 9, has a variable gain amplifier controlled by an automatic gain control circuit. 11. The receiver's IF system, compliant with claim 9, has a variable-gain amplifier circuit digitally controlled by a microcontroller. 12. The receiver's IF system, compliant with claim 9, includes a logarithmic detector with devices to eliminate the effects of gain variation so that the received signal strength indicator is not degraded by the varying gain of a variable gain amplifier circuit. 13. The receiver's IF system, compliant with claim 9, further includes: a downtransform section for converting the second IF signal into a phase-matched and orthogonal baseband signal. 14. The receiver's IF system, in accordance with claim 9, shall include the following: a conversion section for converting the second IF signal to another frequency. 15. The receiver's IF system, in accordance with claim 9, shall include: a voltage-controlled oscillator for providing a tunable frequency signal to the shadow suppression mixing circuit, which shall then mix this tunable frequency signal with the first IF signal in order to change the frequency of the first IF signal. 16. The receiver's IF system, conforming to claim 9, with the first active band-pass filter device, is centered approximately at the first center frequency. 17. The receiver's IF system, in accordance with claim 16, further comprises: a second active-pass filter device centered around the second center frequency; and a switching device for the selective connection of the first and second active-pass filter devices to such variable-gain amplifier and such logarithmic detector (Clause 17, Figure).