A 420 W 100GHz-GBW CMOS Programmable-Gain Amplifier Leveraging the Cross-Coupled Pair Regeneration

Transcription

1 A 420 W 100GHz-GBW CMOS Programmable-Gain Amplifier Leveraging the Cross-Coupled Pair Regeneration M.Sautto 1,2, F.Quaglia 2, G.Ricotti 2 and A. Mazzanti 1 1 University of Pavia - Italy, 2 STMicroelectronics, Milan - Italy. 1 of 18

2 Outline Introduction Circuit description Measurement Conclusions 2 of 18

3 Programmable Gain Amplifier (PGA) PGA Gain [db] Control Signal Key building block in signal processing for ultrasound, wireless, disk drives, etc; Required to provide fixed output swing from a wide range input signal level; Main design challenges: Accurate db-linear gain control; Very high GBW (20MHz BW with 60dB gain leads to 20GHz GBW). 3 of 18

4 Multi-stage PGAs A v, -3dB A v, -3dB A v, -3dB 1 2 N Multi-stage amplifiers commonly exploited for high GBW at low power; Limited gain variation in each stage simplifies db-linear gain control; Penalty of gain compression, particularly at low gain: OP 1dB Penalty OP 1dB Penalty (db) 10dB gain 60dB gain # of Stages 4 of 18

5 PGA Leveraging Regeneration V dd V dd V dd M p-a M p-b V V ing out+ 1 V out- 2 m,in g m,in V in+ C a C b M n-a M n-b Regeneration enables linear-in-db gain control and ultra-wide GBW in a single stage; Negative resistor realized with two cross-coupled pairs; Amplification divided in 4 steps within a clock period T CK. 5 of 18

6 1: Reset V dd V dd V dd V out Reset M p-a M p-b V V ing out+ 1 V outm,in g m,in V in+ t C a C b 1 M n-a M n-b T res T CK t Output capacitors short-circuited; Common mode set to V dd /2 for higher output swing. 6 of 18

7 2: Sampling V dd V dd V dd V out Reset Sampling M p-a M p-b V V ing out+ 1 V outm,in g m,in V in+ t C a C b 1 M n-a M n-b T res T smp T CK t Differential input pre-amplified and sampled. 7 of 18

8 3: Regeneration V dd V dd V dd V out Reset Sampling Regen. M p-a M p-b V V ing out+ 1 V outm,in g m,in V in+ t C a C b 1 M n-a M n-b T res T smp T reg T CK t XCPs on shunt C a,b with negative resistance (-1/g m,xc ); Output rises exponentially with a positive time constant (g m,xc / C a,b ): 8 of 18

9 4: Hold V dd V dd V dd V out Reset Sampling Regen. Hold M p-a M p-b V V ing out+ 1 V outm,in g m,in V in+ t C a C b 1 M n-a M n-b T res T smp T reg T CK T hld t All switches are turned off; Final value of V out stored on output capacitors. 9 of 18

10 Gain Bandwidth Product [Pala-Schonwalder, TCAS-09] Bandwidth trades linearly with gain in db yielding extraordinary GBW improvement; Ex.: Design parameters Regenerative Amplifier Transconductance Amplifier 10 of 18

11 Equivalent Input Noise g m,in g m,xc V in T smp V out T reg I n C a,b T res I n Input transconductor Cross-coupled pair Cross-coupled pairs contribution independent of g m,xc ; Moderate gain in the sampling phase sufficient to make it negligible. Ex.: 11 of 18

12 Timing Generation Cascaded generators to ensure non-overlapping phases; T reg changed linearly controlling I 0 with a simple DAC; Jitter causes SNR limitation: 12 of 18

13 Measurement 180nm CMOS (BCD STMicroelectronics) Power Consumption = 420 W Total Area = 0.03 mm 2 SIGNAL GENERATOR BALUN PGA BUFFER DIFF. PROBE OSCILLOSCOPE 13 of 18

14 Scope Screenshots 14 of 18

15 Gain Measurement Accurate linear-in-db gain control from 15 to 66 db; Max. gain error < 0.6 db; Flat in-band gain, 50MHz maximum bandwidth, 100GHz GBW. 15 of 18

16 Linearity Measurement OP 1dB = -2 45dB gain; THD < -40dB from 10dB back off down; OIP3 = 4.3 dbv calculated from IM3 test. 16 of 18

17 Summary of the Performance JSSC-13 TCAS-14 JSSC-15 This work Technology 65nm 150nm 180nm 180nm Active Area [mm 2 ] Gain Range [db] -13 / / / / 66 db-linear Gain Range [db] OP 1dB [dbm] OIP3 [dbm] / Input Noise [nv/(hz) 0.5 ] Bandwidth [MHz] GBW [GHz] N of stages Power [mw] Highest OP 1dB, state-of-the-art linearity and noise performance; Record GBW with the lowest power consumption. 17 of 18

18 Conclusions A sampled-time PGA leveraging the cross-coupled pair regeneration has been presented; Regeneration naturally leads to db-linear gain control and outperforms the linear GBW trade-off in a single stage; Measurements demonstrate a record 100GHz GBW, the highest OP 1dB with state-of-the-art noise performance and lowest power consumption. 18 of 18