Differential Source Follower having 6dB Gain with Applications to WiGig Baseband Filters

• US 20130076434A1
• Filed: 09/23/2011
• Published: 03/28/2013
• Est. Priority Date: 09/23/2011
• Status: Active Grant

• Current Assignee: Tensorcom Inc
• Original Assignee: Tensorcom Inc
• Inventors: Soe, Zaw
• Granted Patent: US 8,487,695 B2
• Time in Patent Office: Days
• US Class Current: 327/552
• CPC Class Codes: H03F 2203/45528 the FBC comprising one or more passive resistors and being coupled between the LC and the IC
• CPC Class Codes: H03F 2203/45544 the IC comprising one or more capacitors, e.g. coupling capacitors
• CPC Class Codes: H03F 2203/45594 the IC comprising one or more resistors, which are not biasing resistor
• CPC Class Codes: H03F 3/195 in integrated circuits
• CPC Class Codes: H03F 3/301 CMOS common drain output SEPP amplifiers H03F3/3008 takes precedence
• CPC Class Codes: H03F 3/45179 using MOSFET transistors as the active amplifying circuit H03F3/45278 takes precedence
• CPC Class Codes: H03F 3/505 with field-effect devices
• CPC Class Codes: H03H 11/1213 using transistor amplifiers H03H11/1204 takes precedence; parallel-T filters H03H11/1295
• CPC Class Codes: H03H 11/1217 using a plurality of operational amplifiers H03H11/1204 takes precedence; parallel-T filters H03H11/1295
• CPC Class Codes: H03H 11/1286 Sallen-Key biquad
• CPC Class Codes: H03H 3/00 Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
• CPC Class Codes: Y10T 29/49016 Antenna or wave energy "plumbing" making

Abstract

A Sallen-Key filter requires an operational amplifier with a large input impedance and a small output impedance to meet the external filter characteristics. The operational amplifier requires an internal feedback path for stability that limits performance. This invention eliminates the need for internal feedback and increases the gain of a source follower which has characteristics matching the operational amplifier in the Sallen-Key filter. The source follower provides 6 dB of AC voltage gain and is substituted for the operational amplifier in the Sallen-Key filter. The Sallen-Key filter requires a differential configuration to generate all the required signals with their compliments and uses these signals in a feed forward path. Furthermore, since the source follower uses only two n-channel stacked devices, the headroom voltage is maximized to several hundred millivolts for a 1.2V voltage supply in a 40 nm CMOS technology. Thus, the required 880 MHz bandwidth of the Sallen-Key filter can be easily met using the innovative source follower.

Claims

1. An apparatus comprising:

a first device and a second device series coupled between two power supplies;

a first AC input signal coupled to said first device;

a first DC biasing voltage coupled to said first device;

a second AC input signal coupled to said second device;

a second DC biasing voltage coupled to said second device;

an output signal generated between said series coupled devices; and

said first device and said second device are same channel type.

2. The apparatus of claim 1, further comprising:

a first RC network coupling said first AC input signal to said first device;

said first RC network coupling said first DC biasing voltage to said first device;

a second RC network coupling said second AC input signal to said second device; and

said second RC network coupling said second DC biasing voltage to said second device.

3. The apparatus of claim 2, further comprising:

a reference current; and

a third device connected in saturation providing a load for said reference current;

thereby generating said second DC biasing voltage.

4. The apparatus of claim 2, further comprising:

said first device generates a first output signal component; and

said second device generates a second output signal component, whereby

said first output signal component and said second output signal component combine to generate said output signal.

5. The apparatus of claim 4, whereby

said second AC input signal is a complement of said first AC input signal whereby

said second output signal component is a complement of said first output signal component.

6. The apparatus of claim 5, whereby

said output signal is a constructive summation of said first output signal component and said second output signal component.

7. The apparatus of claim 1, whereby

said channel type is an N-MOS device, and

said two power supplies are VDD and GRD.

8. A differential amplifier comprising:

a first upper device and a first lower device series coupled between two power supplies;

a second upper device and a second lower device series coupled between said two power supplies;

a first DC voltage enables said first upper device and said second upper device ;

a second DC voltage regulates current flow in said first lower device and said second lower device;

said first upper device and said second lower device coupled to an AC signal component;

said first lower device and said second upper device coupled to a complement of said AC signal component;

a first output signal between said first upper device and said first lower device; and

a second output signal between said second upper device and said second lower device; and

all said devices are same channel type.

9. The differential amplifier of claim 8, further comprising:

a first RC network coupling said AC signal component to said first upper device;

a second RC network coupling said AC signal component to said second lower device;

a third RC network coupling said complement of said AC signal component to said first lower device; and

a fourth RC network coupling said complement of said AC signal component to said second upper device.

10. The differential amplifier of claim 9, further comprising:

said first RC network coupling said first DC voltage component to said first upper device;

said second RC network coupling said second DC voltage component to said second lower device;

said third RC network coupling said second DC voltage component to said first lower device; and

said fourth RC network coupling said first DC voltage component to said second upper device.

11. The differential amplifier of claim 10, further comprising:

a reference current; and

a first device connected in saturation providing a load for said reference current;

thereby generating said second DC voltage component.

12. The differential amplifier of claim 11, whereby all devices are N-MOS devices.

13. The differential amplifier of claim 8, whereby an output signal is generated between said first output signal and said second output signal.

14. The differential amplifier of claim 8, whereby said two power supplies are VDD and GRD.

15. A differential Sallen-Key filter comprising:

a first AC signal coupled to a first impedance;

a first AC complementary signal coupled to a second impedance;

said first impedance coupled to a third impedance;

said second impedance coupled to a fourth impedance;

said third impedance coupled to a positive input of a first dynamic source follower and to a negative input of a second dynamic source follower;

said fourth impedance coupled to a positive input of said second dynamic source follower and a negative input of said first dynamic source follower; and

an output node of said first dynamic source follower and a complementary output node of said second dynamic source follower generates a differential AC output signal.

16. The differential Sallen-Key filter of claim 15, further comprising:

a fifth impedance coupling said first and third impedances to said output node of said first dynamic source follower;

a sixth impedance coupling said first complementary and fourth impedances to said output node of said second dynamic source follower;

a seventh impedance coupling said positive input of said first dynamic source follower to ground; and

an eighth impedance coupling said positive input of said second dynamic source follower to ground.

17. The differential Sallen-Key filter of claim 16, further comprising:

a plurality of reference currents; and

a plurality of devices connected in saturation providing a load for one of said reference currents and

a DC voltage component;

whereby

said DC voltage component is provided to each dynamic source follower by a different device.

18. The differential Sallen-Key filter of claim 17, further comprising:

two or more differential Sallen-Key filters cascaded in series.

19. The differential Sallen-Key filter of claim 18, whereby all devices are N-MOS devices.

20. The differential Sallen-Key filter of claim 19, whereby

said dynamic source followers are powered by VDD and ground power supplies.