Track and hold circuits for high speed and interleaved ADCs
Improved track and hold (T/H) circuits can help analog-to-digital converters (ADCs) achieve higher performance and lower power consumption. The improved T/H circuits can drive high speed and interleaved ADCs, and the design of the circuits enable additive and multiplicative pseudo-random dither signals to be injected in the T/H circuits. The dither signals can be used to calibrate (e.g., linearize) the T/H circuits and the ADC(s). In addition, the dither signal can be used to dither any remaining non-linearity, and to calibrate offset/gain mismatches in interleaved ADCs. The T/H circuit design also can integrate an amplifier in the T/H circuit, which can be used to improve the signal-to-noise ratio (SNR) of the ADC or to act as a variable gain amplifier (VGA) in front of the ADC.
1. A track-and-hold circuit comprising:
a balun to convert a single-ended signal to a differential signal and to output the differential signal on a first signal path and a second signal path;
a first buffer in the first signal path;
a second buffer in the second signal path;
a first sampling network coupled with an output of the first buffer, wherein the first sampling network includes dither injection;
a second sampling network coupled with an output of the second buffer, wherein the second sampling network includes dither injection; and
a discrete-time amplifier coupled with an output of the first and second sampling networks.
2. The track-and-hold circuit of claim 1 , wherein the balun is to convert the single-ended signal to the differential signal if the single-ended signal has a frequency above a threshold.
3. The track-and-hold circuit of claim 1 , wherein the first sampling network, the second sampling network, and the discrete-time amplifier are operable to provide conversion from a single-ended signal to a differential signal.
4. The track-and-hold circuit of claim 1 , wherein the discrete-time amplifier is an open-loop amplifier.
5. The track-and-hold circuit of claim 1 , further comprising a first matching network that is to match an impedance of the balun to an impedance of the first buffer.
6. The track-and-hold circuit of claim 1 , further comprising a chopper, wherein the chopper is to inject a multiplicative dither.
7. The track-and-hold circuit of claim 1 , wherein the discrete-time amplifier is a closed-loop amplifier.
8. The track-and-hold circuit of claim 1 , further comprising a second matching network that is to match an impedance of the balun to an impedance of the second buffer.
9. A track-and-hold circuit comprising:
a balun that is to receive a single-ended input signal and output a differential output signal at a first output and a second output of the balun based on the single-ended input signal;
a first sampling network with dither injection coupled with the first output of the balun;
a second sampling network with dither injection coupled with the second output of the balun;
a first matching circuit that is to match an impedance of the balun with an impedance of the first sampling network; and
a second matching circuit that is to match an impedance of the balun with an impedance of the second sampling network.
10. The track-and-hold circuit of claim 9 , wherein the balun is to effectively output a single-ended output signal if a frequency of the single-ended input signal is below a threshold frequency.
11. The track-and-hold circuit of claim 10 , wherein the threshold frequency is below 2 gigahertz (GHz).
12. The track-and-hold circuit of claim 9 , wherein the balun is to output the differential output signal if a frequency of the single-ended input signal is above a threshold frequency.
13. The track-and-hold circuit of claim 12 , wherein the threshold frequency is 8 gigahertz (GHz).
14. The track-and-hold circuit of claim 9 , wherein the first matching circuit includes a resistor with a value that is based on a low-frequency impedance match of the balun.
15. The track-and-hold circuit of claim 9 , wherein the first matching circuit includes a capacitor with a value that is based on a transition frequency of the balun.
16. A method, comprising:
converting a single-ended input signal to a differential output signal at a first and second outputs;
sampling, by a first sampling network, the first output;
sampling, by a second sampling network, the second output;
randomly changing a polarity of a differential signal sampled by the first sampling network and the second sampling network; and
amplifying, by a discrete-time amplifier, the differential signal.
17. The method of claim 16 , wherein converting the single-ended input signal to the differential output signal comprises:
effectively outputting a single-ended output signal if a frequency of the single-ended input signal is below a threshold frequency.
18. The method of claim 16 , wherein converting the single-ended input signal to the differential output signal comprises:
outputting the differential output signal if a frequency of the single-ended input signal is above a threshold frequency.
19. The method of claim 16 , further comprising:
injecting an additive dither in one or more of: the first sampling network and the second sampling network; and
calibrating the discrete-time amplifier based on the additive dither.
20. The method of claim 16 , wherein randomly changing the polarity of the differential signal randomizes even-order distortion of the discrete-time amplifier.