Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Patent
1990-12-20
1993-06-15
Eisenzopf, Reinhard J.
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
4552401, 330254, 330 98, H04B 106
Patent
active
052206866
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a tunable resonance amplifier comprising a non-regenerative DC negative feedback loop, which incorporates first and second first-order low-pass RC filters, has a signal path arranged from an input to an output and a feedback path arranged from the output to the input and has a controlled loop gain.
The invention also relates to a frequency synthesis circuit comprising a frequency divider circuit, a phase detector, a loop filter and a voltage-controlled oscillator successively incorporated in a phase-locked loop.
The invention also relates to a superheterodyne receiver with an adaptive IF signal processing.
2. Description of the Related Art
A tunable resonance amplifier of this type is known, for example, from German Patent Specification No. 1,262,466.
A frequency synthesis circuit of this type is known, for example by the type indication LM 7005 of Sanyo.
A superheterodyne receiver of this type is known, for example, from U.S. Pat. No. 3,541,451.
In the signal path from the input to the output the known resonance amplifier successively comprises a voltage signal adding circuit, an inverting controllable voltage amplifier and an RC network composed of a cascade arrangement of the first and the second first-order low-pass RC filters. The output of the resonance amplifier is connected to the adder circuit via the feedback path, resulting in a DC negative feedback loop with a controllable loop gain.
The known resonance amplifier has a bandpass characteristic around a tunable resonance frequency which can be varied by controlling the loop gain. At this resonance or tuning frequency the frequency-dependent transmission of the resonance amplifier is maximum. The passbandwidth of this resonance amplifier is determined by the time constants of the two RC filters and is independent of the loop gain. This provides the possibility of varying. the tuning frequency and hence the frequency location of the pass range at a constant size of the bandwidth.
However, the known resonance amplifier has a selective gain which increases with an increasing tuning frequency, and conversely. Although the increase of the selective gain can be reduced with an increasing tuning frequency by means of an extra integrator arranged in series with the signal path, such an integrator introduces unwanted effects such as, for example a very strong increase of the output signal of the amplifier at a tuning frequency decreasing to zero. The field of use of this known tunable resonance amplifier is comparatively small, also because of this frequency-dependent selective gain. Application in, for example, receiver tuning devices for a tunable channel RF selection of a desired RF reception signal is not possible.
SUMMARY OF THE INVENTION
The invention has for its object to obviate these drawbacks in a simple manner.
According to the invention a tunable resonance amplifier of the type described in the opening paragraph is therefore characterized in that the signal path incorporates one of the two said RC filters and the feedback path incorporates the other RC filter together with the controlled loop gain, or the signal path incorporates the two said RC filters together with one part of the controlled loop gain and the feedback path incorporates the other part of the controlled loop gain.
The invention is based on the recognition that a compensation of the frequency-dependent selective gain of the known resonance amplifier can be obtained without extra components by a suitably chosen distribution of the loop gain and the filter action on the signal and feedback path of the loop.
When using the measure according to the invention, an effective compensation of the frequency-dependent variation of the selective gain of the resonance amplifier is obtained while maintaining a constant bandwidth. This is achieved without the use of extra gain controls and/or circuits such as integrators which increase the costprice and/or even introduce unwanted effects. The tunable resonance a
REFERENCES:
patent: 3792367 (1974-02-01), Fleischer et al.
patent: 3792367 (1974-02-01), Fleischer
patent: 4291276 (1981-09-01), Ida
patent: 4742565 (1988-05-01), Iwahashi
patent: 4776040 (1988-10-01), Ichikawa et al.
De Ruijter Hendricus C.
Kasperkovitz Wolfdietrich G.
Belzer Christine K.
Eason Leroy
Eisenzopf Reinhard J.
U.S. Philips Corporation
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