Very high frequency mixer

• US 4,845,389 A
• Filed: 03/01/1988
• Issued: 07/04/1989
• Est. Priority Date: 03/06/1987
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Gamand, Patrice, Pyndiah, Ramesh
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Roseen, Richard
• Application Number:
  US07/162,522
• Time in Patent Office: 490 Days
• Field of Search: 307/529, 307/572, 333/218, 333/16, 333/160
• US Class Current: 327/113
• CPC Class Codes: H03D 2200/0027 including arrangements for assuring the same gain in two paths
• CPC Class Codes: H03D 7/125 with field effect transistors
• CPC Class Codes: H03D 9/0675 using field effect transistors H03D9/0683 takes precedence

Abstract

A mixer of the two-transistor type (T₁, T₂) arranged in series by a source S₂ and a drain D₁. A Gate G₁ receives a radio frequency signal RF and a gate G₂ a local oscillator signal L0. Matching networks R₁ and R₂ are provided for the respective signals RF and L0. One element of the network R₃ positioned at the output (drain D₂ of the transistor T₂) restores a short-circuit at the frequency f_L0 of the local oscillator. The instability of the input G₂ of the transistor T₂ is compensated for by an inductor element L inserted between the junction point of the source S₂ and the drain D₁ and the common-mode pole.

Claims

1. A very high frequency mixer comprising a first and a second field effect transistor, one of the transistors being intended to receive at its gate a local oscillator signal and the other transistor a radio-frequency input signal, the first transistor having a source connected to a first supply voltage pole, and a drain connected at a junction point to a source of the second transistor, and a drain of the second transistor being connected to a second supply voltage pole via a resistor, characterized in that the drain of the second transistor is charged by a circuit element realizing a short-circuit at the frequency of the local oscillator signal, and in that the mixer further comprises an inductor element inserted between the junction point and a common-mode pole, the inductor element being selected such as to compensate for drain-source capacitances of the two transistors and thus to stabilize the input at the gate of a second transistor.

2. A mixer as claimed in claim 1, wherein the first transistor is intended to receive at its gate the radio-frequency signal and the second transistor is intended to receive at its gate the local oscillator signal.

3. A mixer as claimed in claim 2, the gate of the first transistor comprises a circuit for matching the signal which it is intended to receive.

4. A mixer as claimed in claim 3, wherein the gate of the second transistor (T₂) comprises a matching circuit for the signal which it is intended to receive.

5. A mixer as claimed in one of the preceding claims 1-4 wherein the inductor element has a value L such that:

##EQU8## with;

fT₂ being the cut-off frequency at 0 dB of the second transistor,

Cgs₂ being the gate source capacitor of the second transistor Cds₁ and Cds₂ being drain-source capacitors of the first and second transistors, respectively,

gd₁ and gd₂ being conductances of the first and second transistors, respectively,

and Cds=CDs₁ +Cds₂, gd=gd₁ +gd₂

ω

.sub. = π

F₀ F_o =the highest local oscillator frequency.

6. A mixer as claimed in claim 5, wherein the inductor element L is chosen such as to realize a bandpass filter whose central frequency is situated substantially within the useful receiver band, so as to filter out noise situated in the intermediate-frequency band and generated by the first transistor T₁.

7. A mixer as claimed in claim 5, wherein the inductor element has a value L in the neighborhood of LO with:

##EQU9## where w_RF =2π

F_RF, F_RF denoting the frequency of the input signal and F_RF =F_LO.