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

摘要

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.

主权项

1. 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.