Ying-Zu Lin

A 10-bit 50-MS/s SAR ADC With a Monotonic Capacitor Switching Procedure

This paper presents a low-power 10-bit 50-MS/s successive approximation register (SAR) analog-to-digital converter (ADC) that uses a monotonic capacitor switching procedure. Compared to converters that use the conventional procedure, the average switching energy and total capacitance are reduced by about 81% and 50%, respectively. In the switching procedure, the input common-mode voltage gradually converges to ground. An improved comparator diminishes the signal-dependent offset caused by the input common-mode voltage variation. The prototype was fabricated using 0.13-¿m 1P8M CMOS technology. At a 1.2-V supply and 50 MS/s, the ADC achieves an SNDR of 57.0 dB and consumes 0.826 mW, resulting in a figure of merit (FOM) of 29 fJ/conversion-step. The ADC core occupies an active area of only 195 × 265 ¿m2.

A 10b 100MS/s 1.13mW SAR ADC with binary-scaled error compensation

In recent years, due to the improvements in CMOS technologies, medium resolution (8 to 10b) SAR ADCs have been able to achieve sampling rates of several tens of MS/s with excellent power efficiency and small area [1]–[4]. When the sampling rate increases, the SAR ADCs suffer from settling issues. In a typical 10b 100MS/s ADC, when the sampling settling time, comparator active time and SAR logic delay are subtracted from each period, the DAC settling time has to be less than 0.4ns in each bit cycle. Such a short time interval is not sufficient for the capacitive DAC to stabilize because the increasing interconnect line impedance in advanced processes slows down the charge transfer, especially in the longest routing path of the DAC capacitor network. Furthermore, the reference voltage sinks noise and line coupling also affects the settling. A non-binary SAR can tolerate DAC settling error at the cost of increased design complexity and hardware overhead [1]. This paper reports a 10b SAR ADC that uses binary-scaled DAC networks for settling error compensation. The ADC achieves 100MS/s while consuming only 1.13mW.

A 9-bit 150-MS/s 1.53-mW subranged SAR ADC in 90-nm CMOS

This paper reports a subranged SAR ADC consisting of a 3.5-bit flash coarse ADC, a 6-bit SAR fine ADC, and a differential segmented capacitive DAC. The flash ADC controls thermometer MSBs of the DAC and SAR ADC controls the binary LSBs. The segmented DAC improves DNL during MSB transitions. The merged switching of MSB capacitors enhances operation speed. The 9-bit 150-MS/s ADC consumes 1.53 mW from a 1.2-V supply. The ENOB is 8.69 bit and ERBW is 100 MHz. The FOMs at 1.2 V, 150 MS/s and 1 V, 100 MS/s are 24.7 and 17.7 fJ/conversion-step, respectively. At 1.3-V supply voltage, the sampling rate achieves 200 MS/s.

An Asynchronous Binary-Search ADC Architecture With a Reduced Comparator Count

This paper reports an asynchronous binary-search analog-to-digital converter (ADC) with reference range prediction. An original N-bit binary-search ADC requires 2N - 1 comparators while the proposed one only needs 2N - 1 ones. Compared to the (high speed, high power) flash ADC and (low speed, low power) successive approximation register ADC, the proposed architecture achieves the balance between power consumption and operation speed. The proof-of-concept 5-bit prototype only consists of a passive track-and-hold circuit, a reference ladder, 9 comparators, 56 switches and 26 static logic gates. This compact ADC occupies an active area of 120 × 50 μm2 and consumes 1.97 mW from a 1-V supply. At 800 MS/s, the effective number of bits is 4.40 bit and the effective resolution bandwidth is 700 MHz. The resultant figure of merit is 116 fJ/conversion-step.

A 5-bit 3.2-GS/s Flash ADC With a Digital Offset Calibration Scheme

In high-speed Flash analog-to-digital converters (ADCs), preamplifiers are often placed in front of a comparator to reduce metastability errors and enhance comparison speed. The accuracy of a Flash ADC is mainly limited by the random offsets of preamplifiers and comparators. This paper presents a 5-b Flash ADC with a digital random offset calibration scheme. For calibration, programmable resistive devices are used as the loading devices of the second-stage preamplifiers. By adjusting the calibration resistors, the input-referred offset voltage of each comparator is reduced to be less than 1/2 LSB. Fabricated in a 0.13-¿m CMOS process, experimental results show that the ADC consumes 120 mW from a 1.2-V supply and occupies a 0.18- mm2 active area. After calibration, the peak differential non-linearity (DNL) and integral non-linearity (INL) are 0.24 and 0.39 LSB, respectively. At 3.2-GS/s operation, the effective number of bits is 4.54 b, and the effective resolution bandwidth is 600 MHz. This ADC achieves figures of merit of 3.07 and 4.30 pJ/conversion-step at 2 and 3.2 GS/s, respectively.

A 1V 11fJ/conversion-step 10bit 10MS/s asynchronous SAR ADC in 0.18µm CMOS

This paper presents a 10-bit SAR ADC using a variable window function to reduce the unnecessary switching in DAC network. At 10-MS/s and 1-V supply, the ADC consumes only 98 µW and achieves an SNDR of 60.97 dB, resulting in an FOM of 11 fJ/Conversion-step. The prototype is fabricated in a 0.18µm CMOS technology.

A 5b 800MS/s 2mW asynchronous binary-search ADC in 65nm CMOS

Digital wireless communication applications such as UWB and WPAN necessitate low-power high-speed ADCs to convert RF/IF signals into digital form for subsequent baseband processing. Considering latency and conversion speed, flash ADCs are often the most preferred option. Generally, flash ADCs suffer from high power consumption and large area overhead. On the contrary, SAR ADCs have low power dissipation and occupy a small area. However, a SAR ADC needs several comparison cycles to complete one conversion, which limits its conversion speed. The highest single-channel operation speed of previously reported SAR ADCs is 625MS/s [1]. The ADC in [1] utilizes a 2b/step structure. For non-multi-bit/step SAR ADCs, the highest reported conversion rate is 300MS/s [2]. The structure of a comparator-based binary-search ADC is between that of flash and SAR ADCs [3]. Compared to a flash ADC (high speed, high power) and a SAR ADC (low speed, low power), a binary-search ADC achieves balance between operation speed and power consumption. This paper reports a 5b asynchronous binary-search ADC with reference-range prediction. The maximum conversion speed of this ADC is 800MS/s at a cost of 2mW power consumption.

A 10-bit 12-MS/s successive approximation ADC with 1.2-pF input capacitance

This paper reports a successive-approximation analog-to-digital converter (ADC) with low input capacitance. The 10-bit prototype is fabricated in a 0.13-µm CMOS process. Compared to conventional successive approximation ADCs, the proposed ADC reduces the input capacitance to 1.2 pF for 10-bit resolution. At 12 MS/s and 1.2-V supply, this ADC consumes 0.32 mW and achieves an SNDR of 50.89 dB, resulting in an FOM of 95 fJ/Conversion-step.

A 0.9-V 11-bit 25-MS/s binary-search SAR ADC in 90-nm CMOS

This paper presents a new subrange analog-to-digital converter (ADC): a binary-search coarse ADC + a SAR fine ADC. The binary-search ADC improves conversion speed and gives coarse capacitors longer settling time. This ADC uses an RC hybrid DAC to reduce the unit capacitor count by 2. The rotation function of coarse capacitors enhances capacitor array linearity. The prototype in 90-nm CMOS only occupies an active area of 0.06 mm2. From a 0.9-V supply, the power consumption is 0.32 and 0.58 mW at 10 and 25 MS/s, respectively. At 10 MS/s, the peak ENOB is 10.2 bit. At 25 MS/s, the peak ENOB is 9.9 bit and FOM is 29 fJ/conversion-step.

A 5-bit 4.2-GS/s flash ADC in 0.13-μm CMOS

A compact 5-bit flash ADC is designed and fabricated in TSMC 0.13-μm CMOS process. Resistive averaging network and interpolation are discussed and analyzed for power reduction. This proposed ADC consumes 180 mW from a 1.2 V supply and occupies 0.16 mm2 active area. Operating at 3.2 GS/s, the ENOB is 4.44 bit and ERBW 1.65 GHz. At 4.2 GS/s, the ENOB is 4.20 bit and ERBW 1.75 GHz. This ADC achieves FOMs of 2.51 and 2.80 pJ/conversion-step at 3.2 and 4.2 GS/s, respectively.