Integral nonlinearity error

MAX11162

edge. The SDI input of each ADC in the chain is used to transfer conversion data from the previous ADC into the internal shift register of the next ADC, thus allowing for data to be clocked through the multichip chain on each SCLK falling edge. With busy indicator mode selected, the busy bit from each part is not chained on the first falling SCLK edge in the readout pattern. Consequently, the number of falling SCLKs needed to read back all data from N ADCs is 16 × N + 1 falling edges.

In daisy-chain mode, the maximum conversion rate is reduced due to the increased readback time. For instance, with a 6ns digital host setup time and 3V interface, up to four MAX11162 devices running at a conversion rate of 217ksps can be daisy-chained on a 3-wire port.

Layout, Grounding, and Bypassing

For best performance, use PCBs with ground planes. Ensure that digital and analog signal lines are separated from each other. Do not run analog and digital lines parallel to one another (especially clock lines), and avoid running digital lines underneath the ADC package. A single solid GND plane configuration with digital signals routed from one direction and analog signals from the other provides the best performance. Connect the GND pin on the MAX11162 to this ground plane. Keep the ground return to the power supply low impedance and as short as possible for noise-free operation.

A 4.7nF C0G (or NPO) ceramic chip capacitor should be placed between AIN+ and the ground plane as close as possible to the MAX11162. This capacitor reduces the inductance seen by the sampling circuitry and reduces the voltage transient seen by the input source circuit. If AINis to be used for remote sense, put a matching 4.7nF C0G ceramic capacitor as close to this pin as well to minimize the effect to the inductance in the remote sense line.

For best performance, decouple the REF output to the ground plane with a 16V, 10µF or larger ceramic chip capacitor with a X5R or X7R dielectric in a 1210 or smaller case size. Ensure that all bypass capacitors are connected directly into the ground plane with an independent via.

Bypass VDD and OVDD to the ground plane with 0.1FF ceramic chip capacitors on each pin as close as possible to the device to minimize parasitic inductance. Add at least one bulk 10FF decoupling capacitor to VDD and OVDD per PCB. For best performance, bring a VDD power plane in on the analog interface side of the MAX11162 and a OVDD power plane from the digital interface side of the device.

16-Bit, 500ksps, +5V Unipolar Input, SAR ADC, in Tiny 10-Pin µMAX

Integral Nonlinearity

Integral nonlinearity (INL) is the deviation of the values on an actual transfer function from a straight line. For these devices, this straight line is a line drawn between the end points of the transfer function, once offset and gain errors have been nullified.

Differential Nonlinearity

Differential nonlinearity (DNL) is the difference between an actual step width and the ideal value of 1 LSB. For these devices, the DNL of each digital output code is measured and the worst-case value is reported in the Electrical Characteristics table. A DNL error specification of less than ±1 LSB guarantees no missing codes and a monotonic transfer function.

Offset Error

For the MAX11162, the offset error is defined at the code transition of 0x0000 to 0x0001. The code transition of 0x0000 to 0x0001 should occur with an analog input voltage 0.5 LSB above GND or +38µV. The offset error is defined as the deviation between the actual analog input voltage required to produce the code transition of 0x0000 to 0x0001 and the ideal analog input of +38µV, expressed in LSBs.

Gain Error

Gain error is defined as the difference between the change in analog input voltage required to produce a top code transition minus a bottom code transition, subtracted from the ideal change in analog input voltage on VREF x (65534/65536). For the MAX11162, top code transition is 0xFFFE to 0xFFFF. The bottom code transition is 0x0000 and 0x0001. For the MAX11162, the analog input voltage to produce these code transitions is measured and then the gain error is computed by subtracting VREF x (65534/65536) from this measurement.

Signal-to-Noise Ratio

For a waveform perfectly reconstructed from digital samples, signal-to-noise ratio (SNR) is the ratio of the fullscale analog input power to the RMS quantization error (residual error). The ideal, theoretical minimum analog- to-digital noise is caused by quantization noise error only and results directly from the ADC’s resolution (N bits):

SNR = (6.02 x N + 1.76)dB

In reality, there are other noise sources besides quantization noise: thermal noise, reference noise, clock jitter, etc. SNR is computed by taking the ratio of the power signal to the power noise, which includes all spectral components

MAX11162

not including the fundamental, the first five harmonics, and the DC offset.

Signal-to-Noise Plus Distortion

Signal-to-noise plus distortion (SINAD) is the ratio of the fundamental input frequency’s power to the power of all the other ADC output signals:

Effective Number of Bits

The effective number of bits (ENOB) indicates the global accuracy of an ADC at a specific input frequency and sampling rate. An ideal ADC’s error consists of quantization noise only. With an input range equal to the full-scale range of the ADC, calculate the ENOB as follows:

ENOB = SINAD −1.76 6.02

Total Harmonic Distortion

Total harmonic distortion (THD) is the ratio of the power contained in the first five harmonics of the converted data to the power of the fundamental. This is expressed as:

where P1 is the fundamental power and P2 through P5 is the power of the 2ndthrough 5th-order harmonics.

16-Bit, 500ksps, +5V Unipolar Input, SAR ADC, in Tiny 10-Pin µMAX

Spurious-Free Dynamic Range

Spurious-free dynamic range (SFDR) is the ratio of the power of the fundamental (maximum signal component) to the power of the next-largest frequency component.

Aperture Delay

Aperture delay (tAD) is the time delay from the sampling clock edge to the instant when an actual sample is taken.

Aperture Jitter

Aperture jitter (tAJ) is the sample-to-sample variation in aperture delay.

Small-Signal Bandwidth

A small -20dBFS analog input signal is applied to an ADC in a manner that ensures that the signal’s slew rate does not limit the ADC’s performance. The input frequency is then swept up to the point where the amplitude of the digitized conversion result has decreased 3dB.

Full-Power Bandwidth

A large -0.5dBFS analog input signal is applied to an ADC, and the input frequency is swept up to the point where the amplitude of the digitized conversion result has decreased by 3dB. This point is defined as full-power input bandwidth frequency.