Attenuation circuit

#This invention relates generally to attenuation circuits, particularly as used in an IF section of a radio receiver.

#Radio receivers receive and process radio frequency transmitted energy signals to yield, generally, audible information. Typically, the originally received RF signal will be converted to an intermediate frequency (IF) signal prior to reducing the desired signal information yet further to audio levels. Various signal processing functions may occur at the IF level, including signal attenuation as may be necessary to prevent the signal from exceeding a threshold level.

#With reference to FIG. 1A, one prior art attenuation circuit for providing such attenuation can be seen to include two coupling capacitors (A and B), a current source (C), and a diode (D). Typically, diodes present an impedance of 26 ohms at one milliamp. This impedance, however, will diminish as current flow through the diode increases For example, with 10 milliamps flowing through such a diode, the impedance presented by the diode will be approximately 2.6 ohms. Therefore, by regulating the flow of current through the diode (D) by appropriate control of the current source (C), the impedance of the diode (D) can be manipulated to govern attenuation of a signal as received at the input.

#These and other attributes of the invention will become more clear upon making a thorough review and study of the following description of the best mode for carrying out the invention, particularly when reviewed in conjunction with the drawings, wherein:

#FIGS. 1A and B comprise depictions of prior art circuits;

#FIG. 2 comprises a block diagram view of a first embodiment;

#Referring now to the drawings, and in particular to FIG. 2, a first embodiment of the invention can be seen as depicted generally by the numeral 10. This first embodiment (10) includes an input (11), an attenuator (12), a dynamic reference signal unit (13), a comparison unit (14), a control input (16), and an attenuator output (17). The attenuator (12) receives an input signal at the input (11), which signal is to be attenuated as necessary. The degree of attenuation depends in part upon the control input signal as received by the control input (16). The dynamic reference signal unit (13) provides a reference signal as a function of a DC variable signal that effects the accuracy of the attenuator signal. The comparison unit (14) compares the attenuator signal with the reference signal to provide a signal at the attenuator output (17) that substantially comprises the former minus the latter signal.

#Referring now to FIG. 3, a somewhat more detailed depiction of the first embodiment (10) will be provided. The attenuator (12) can be comprised of two diodes (18 and 19) and a capacitor (21). The capacitor (21) couples the input (11) to an attenuation node (22). The first diode (18) connects between the attenuation node (22) and the control input (16). The second diode (19) connects between the attenuation node (22) and a lower bias (23).

#The dynamic reference signal unit (13) can be similarly comprised of two diodes (26 and 27). The first diode (26) connects between the control input (16) and a reference node (28). The remaining diode (27) connects between the reference node (28) and the lower bias (23).