Sampling Keep (T / H) demodulator instead of conventional signal demodulator advantages and disadvantages

This article discusses the problem of using tracking holding signal demodulators in the chopping stabilization amplifier instead of the traditional signal demodulator. With this setting and average function, it can provide offset cancellation without low pass filters, and the residual offset generated by the input spike can be ignored. Noise analysis shows that although the noise reduction can be reduced by using the maximum duty cycle and the minimum amplifier bandwidth, the T / H demodulator reduces the white noise signal noise ratio (SNR). introduce The chopper stabilization of the amplifier is a well-known technique for reducing input DC offset and low frequency input noise, which typically reducing the performance of the precision DC amplifier. Figure 1 shows the basic principle. Figure 1 Traditional chopping stabilization amplifier First, the input signal multiply the frequency ƒclk of the unit symmetric square wave function S1 (t), and then enlarges through the gain amplifier, and the g is multiplied by the switch function S2 (T) similar to S1 (T), and finally low-pass filtering. The first multiplication converts the input signal spectrum to a high frequency region, and the second multiplication is to recover the amplified raw signal by bringing the signal demodulation backbest. On the other hand, the DC offset and low frequency noise components of the input reference amplifier are only treated only by second multiplication. For example, the DC offset is converted to an HF square wave function, which is fully attenuated by the low pass filter. The multiplication function is usually achieved by a simple metal oxide semiconductor switch controlled by the clock signal. The problem of conventional choppers is that parasitic offsets may occur due to transients of the first multiplication switch. These offsets are passed through a low pass filter without cancellation. Another problem is to attenuate low-pass filtering required for residual square corruption due to offsets. This is particularly severe in the monopolar chopper, in a single pole chopper, the multi-pole LP filter requires a considerable silicon area. Next, we describe the advantages and disadvantages of the demodulator based on the sampling hold (T / H), replace the conventional signal demodulator. Sampling keep signal demodulator Let us assume that the bandwidth of the input signal VSG of the chopping stabilizer amplifier is limited to the Nyquist frequency (ƒclk/ 2), and the amplifier is noise. Compared to TCLK / 2, residual disorders due to the short transient peak peak of the input switch can be significantly reduced by using the amplifier narrowband or a band pass filter that includes a center frequency to be ƒCLK. In the case where the chopper is operated with a relatively high frequency and the input spike duration is no longer ignored compared to TCLK / 2, the amplifier is widening and the S2 (T) is less than 50%. Switching functions, similar results can be obtained. The cycle, as shown in FIG. 2, in which the output is zero in the Δt interval (amplified peaks). Figure 2 Remove the input spike Edit: hfy, read full text