Integrated circuits for voltage controlled oscillators

• US 6,140,884 A
• Filed: 03/26/1999
• Issued: 10/31/2000
• Est. Priority Date: 03/31/1998
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: James, John Coulson, Harpham, Simon Lewis
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Glenn, Kimberly E
• Application Number:
  US09/277,488
• Time in Patent Office: 585 Days
• Field of Search: 331/117 R, 331/111, 331/116 R, 331/116 FE, 331/117 FE, 331/117 D, 331/167, 331/175
• US Class Current: 331/117.00R
• CPC Class Codes: H03B 2200/0034 including a buffer amplifier
• CPC Class Codes: H03B 2202/05 Reduction of undesired oscillations through filtering or through special resonator characteristics
• CPC Class Codes: H03B 2202/07 Reduction of undesired oscillations through a cancelling of the undesired oscillation
• CPC Class Codes: H03B 5/1209 the amplifier having two current paths operating in a differential manner and a current source or degeneration circuit in common to both paths, e.g. a long-tailed pair. H03B5/1215 takes precedence
• CPC Class Codes: H03B 5/1231 the amplifier comprising one or more bipolar transistors
• CPC Class Codes: H03B 5/1243 the means comprising voltage variable capacitance diodes
• CPC Class Codes: H03B 5/1296 the feedback circuit comprising a transformer

Abstract

An integrated circuit (shown below dashed line A--A) for a voltage controlled oscillator comprises a first transistor (T₁) having its collector coupled to a first port (Port 1) via a filter comprising a capacitor (C_f) and an inductor (L_f) and its emitter coupled to the emitter of a second transistor (T₂) whose collector is coupled to a second port (Port 2). The collector of the first transistor is also coupled via a capacitive divider (C₁, C₂) to the base of the second transistor. The base of the first transistor is AC decoupled (C₃). The emitters of the first and second transistors are fed by a current source (I₁). A capacitor (C_s) connects the base of the second transistor to the first port. The first and second ports are for connection to an external resonator (L₁, D₁, C_p, L_p) (shown above dashed line A--A) where C_p and L_p are parasitic capacitances and inductances respectively, the latter being typically bond wires connecting the ports to the rest of the external resonator. The filter (C_f, L_f) causes the circuit to exhibit negative impedance across the first and second ports. A VCO embodying the invention is tunable across the intended frequency range without exhibiting frequency hopping or mode switching.

Claims

1. An integrated circuit for a voltage controlled oscillator (VCO) comprising:

first and second ports (Port 1, Port

     2) for connection to an external resonator (L₁, D₁, C_p, L_p),

first and second transistors (T₁, T₂) each having first and second controlled electrodes and a control electrode,

the first transistor (T₁) having its first controlled electrode coupled via a filter (C_f, L_f) to the first port (Port

     1), the resonant frequency of the filter being within the intended frequency range of the VCO,

the second transistor (T₂) having its first controlled electrode coupled to the second port (Port

     2),

means (C₁) for AC coupling the first controlled electrode of the first transistor (T₁) to the control electrode of the second transistor (T₂),

the second controlled electrodes of the first and second transistors being coupled together and fed by a current source (I₁), and

means (C₃) for decoupling the control electrode of the first transistor, wherein, in operation, negative impedance is exhibited between the first and second ports.

2. An integrated circuit as claimed in claim 1 comprising a capacitor (C_s) coupled between the control electrode of the second transistor (T₂) and the first port (Port 1), the capacitor forming, in operation, a series resonant circuit with the external resonator.

3. An integrated circuit as claimed in claim 1 wherein the AC coupling means comprises a capacitor (C₁) forming part of a capacitive divider (C₁, C₂).

4. An integrated circuit as claimed in claim 1 comprising a buffer transistor, (T₃) having a control electrode coupled to the first controlled electrode of the first transistor, for providing output at a controlled electrode thereof.

5. A VCO comprising an integrated circuit as claimed in claim 1, and an external resonator (L₁, D₁, C_p, L_p) coupled to the first and second ports.

6. A VCO as claimed in claim 5 wherein the external resonator comprises a variable capacitance diode (D₁) having a terminal for receiving a variable voltage (V_v) for controlling the VCO frequency.