US 4,520,507 A · Low noise CATV converter

Abstract

A low noise frequency converter particularly adapted for the large bandwidth environment encountered in extended bandwidth cable television (CATV) systems is disclosed. The CATV converter includes an upconverter/downconverter combination for translating the received RF signal to an intermediate frequency (IF) carrier signal. A first IF signal is generated by heterodyning the received RF signal with the output of a voltage controlled oscillator in a first double balanced mixer. The upconverted signal thus produced is then mixed in a second double balanced mixer with the reference output of a second local oscillator to provide a fixed, downconverted second IF carrier signal. The upconverter portion of the CATV converter includes a pin diode attenuator between an RF amplifier and the first double balanced mixer. The pin diode attenuator is driven by the RF amplifier and is regulated by the signal receiver's automatic gain control (AGC) system permitting signal level to be increased at a faster rate than noise figure resulting in an improved converter signal-to-noise ratio and improved large signal handling capability. The downconverter portion of the CATV converter includes a double balanced diode mixer between the first IF amplifier and the second IF amplifier. With the double balanced diode mixer for the second mixer in the downconverter section, cross-modulation and intermodulation distortion from adjacent channels is reduced. In addition, the double balanced diode mixer provides an improved overall noise figure due to its lower noise performance than that available with either a single ended diode mixer or active mixer.

Claims11

Dependent claims

In a CATV signal converter coupled to a signal processing circuit wherein a received CATV signal is initially upconverted to a first, higher IF signal and then downconverted to a second, lower IF signal and then provided to said signal processing circuit, said signal processing circuit including an automatic gain control (AGC) system responsive to the level of said second IF signal, a frequency upconverter comprising:

a low noise wideband RF amplifier having a controllable operating point for amplifying said received CATV signal wherein the gain and terminal impedance of said amplifier are maintained substantially constant over a wide frequency band;
variable attenuation means coupled to said RF amplifier for the selective attenuation of the amplified CATV signal;
an oscillator for generating a reference signal having a selected frequency;
a mixer coupled to said variable attenuation means and said oscillator for mixing said amplified CATV and reference signals to produce said first, higher IF signal;
and
means coupling said AGC system to said RF amplifier and said variable attenuation means for controlling the operating point of said RF amplifier and for controlling the amount of attenuation of the amplified CATV signal by said variable attenuation means in response to an AGC control signal provided by said signal processing circuit.

3 more elements

Dependencies are inferred from the claim text.

Low noise CATV converter

Life of this patent

Low noise CATV converter

Life of this patent

Abstract

Claims11