SOLID-STATE VHF ATTENUATOR AND TV RECEIVER

• US 3,619,786 A
• Filed: 05/28/1969
• Issued: 11/09/1971
• Est. Priority Date: 12/30/1966
• Status: Expired due to Term

• Current Assignee: Donald L. Wilcox
• Original Assignee: Donald L. Wilcox
• Inventors: Wilcox, Donald L.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Weinstein, Kenneth W.
• Application Number:
  US04/859,600
• Time in Patent Office: 895 Days
• Field of Search: 325/400,411,414,415,380,387,362 333/81
• US Class Current: 455/248.1
• CPC Class Codes: H03F 2200/63 the amplifier being suitable for CATV applications
• CPC Class Codes: H03G 1/0058 PIN-diodes
• CPC Class Codes: H03G 3/3057 using at least one diode as controlling device

Abstract

Disclosed are television receivers of the type having voltagecontrolled AC signal attenuators including diodes which are advantageously suitable for use as an automatic gain control in a television receiver, for example, or for attenuating any UHF or high-frequency signals. These novel attenuators, when incorporated in a television receiver, (1) substantially eliminate pole-shifting distortion by permitting the RF and IF amplifiers to be operated at one biaspoint, (2) protect the amplifier from overload by preamplification attenuation of the incoming signals, (3) improve system cross modulation, (4) permit use of field effect transistors, and (5) assure minimum degradation of the amplifier noise figure.

Claims

1. A television receiver comprising in combination:

a. first and second attenuator means, each including a plurality of current controlled variable impedance members having an impedance which decreases from a relatively high value to a relatively low value as the forward current through said members increases from substantially zero;

b. balum input means for coupling AC signals to the input of said first attenuator means;

c. RF amplifier means coupled to the output of said first attenuator means;

d. mixer means coupled to the output of said RF amplifier means and to the output of a local oscillator means for producing selected IF signals, said mixer means having its output coupled to the input of said second attenuator means;

e. IF amplifier means coupled to the output of said second attenuator means and having its output coupled to the input of a demodulation and display network for producing AGC signals which are direct functions of the amplitude of said IF signals; and

f. AGC amplifier means coupled to the output of said demodulation and display network and having two output circuits respectively coupled to the inputs of said first and second attenuator means;

wherein g. said RF and IF amplifiers are operated at a common bias point for eliminating pole-shifting distortion; and

wherein h. said first and second attenuator means provide relatively low attenuation when said IF signals are below a predetermined level and progressively increase attenuation as the amplitude of said IF signals progressively increase.

2. bias said second diode to a forward current value that provides minimum impedance when said bias terminal is at one voltage level;

wherein h. when the bias voltage at said one terminal varies in a predetermined manner, the forward current through said second diode progressively decreases and the forward current through said first and third diodes progressively increases; and

wherein i. for any set of forward current conditions the attenuation of said AC signals through said attenuator means will be a function of the ratio of the resistance of said second diode to the resistance of said first diode and of the ratio of the impedance of said output circuit to the impedance of said third diode.

3. The television receiver of claim 2 wherein the impedance of said second diode approaches the impedance of said AC signals as the impedance of said first diode becomes relatively large to prevent the reflection of energy from said first and second attenuator means.

4. said first resistor and said first and third diodes are each AC coupled to ground;

and wherein d. said first, second and third diodes can be selectively biased by selectively varying said first, second, third and fourth voltage supplies.

5. The television receiver of claim 1 wherein said first and second attenuator means each include;

a. input and output circuits;

b. first, second, and third diodes, each having an impedance which decreases from a maximum to a minimum value as the forward current through said diodes increases from zero;

c. said first and second diodes having common terminals connected together to form an input junction;

d. said second and third diodes having common terminals connected together to form an output junction;

e. first and second AC coupling means respectively coupling said first and third diodes to ground;

f. first and second DC isolation means respectively coupling said input and output junctions to said input and output circuits; and

g. a biasing network including at least one variable bias voltage terminal connected so as to

6. The television receiver of claim 5 wherein said first, second and third diodes are PIN diodes.

7. The television receiver of claim 5 wherein:

a. said first and second AC coupling means each include a feedthroUgh capacitor;

b. said first and second DC isolation means each include a coupling capacitor; and

c. said biasing network includes;

8. The television receiver of claim 5 wherein variation of said second voltage supply proportionately varies the attenuation characteristics of said first and second attenuator means.