US 8,803,596 B2 · Differential source follower having 6dB gain with applications to WiGig baseband filters

Abstract

Sallen-Key filters require an operational amplifier with a large input impedance and a small output impedance to meet the external filter characteristics. This invention eliminates the need for internal feedback path for stability 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 complements 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.

Claims20

Dependent claims

An apparatus with at least one differential Sallen-Key filter comprising:

a first impedance couples a first signal to a third impedance;
a second impedance couples a complementary first signal to a fourth impedance;
a positive input of a first dynamic source follower and a negative input of a second dynamic source follower coupled to said first impedance by said third impedance;
a positive input of said second dynamic source follower and a negative input of said first dynamic source follower coupled to said second impedance by said fourth impedance;
and
a differential output signal generated between an output node of said first dynamic source follower and an output node of said second dynamic source follower.

3 more elements

A differential Sallen-Key filter comprising:

a first output impedance of a differential output circuit configured to provide a first output signal;
a second output impedance of said differential output circuit configured to provide a complement of said first output signal, wherein
a first differential output signal is generated between said first output signal and said complement of said first output signal;
a first impedance couples said first output signal to a positive input of a first dynamic source follower and a negative input of a second dynamic source follower;
and
a second impedance couples said complement of said first output signal to a negative input of said first dynamic source follower and a positive input of said second dynamic source follower, wherein
a second differential output signal is generated between a first output of said first dynamic source follower and a first output of said second dynamic source follower.

4 more elements

A method of forming a differential output signal for at least one Sallen-Key filter comprising the steps of:

coupling a first impedance between a first signal and a third impedance;
coupling a second impedance between a complementary first signal and a fourth impedance;
coupling said third impedance between a positive input of a first dynamic source follower and said first impedance;
coupling said third impedance between a negative input of a second dynamic source follower and said first impedance;
coupling said fourth impedance between a positive input of said second dynamic source follower and said second impedance;
coupling said fourth impedance between a negative input of said first dynamic source follower and said second impedance;
and
generating said differential output signal between an output node of said first dynamic source follower and an output node of said second dynamic source follower.

5 more elements

Dependencies are inferred from the claim text.

Differential source follower having 6dB gain with applications to WiGig baseband filters

Life of this patent

Differential source follower having 6dB gain with applications to WiGig baseband filters

Life of this patent

Abstract

Claims20